SCHOOL  OF  MEDICINE 
LIBRARY 


From  the  Library  of 
Dr»  William  S.  Kuder 


n 


'^fiMoJ. 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

Microsoft  Corporation 


http://www.archive.org/details/anatomyofbrainspOOsantrich 


ANATOMY 

OF   THE 

BRAIN  AND  SPINAL  CORD 


SANTEE 


ANATOMY 

OF   THE 

BRAIN  AND   SPINAL  CORD 

WITH  SPECIAL  REFERENCE  TO 

MECHANISM  AND  FUNCTION 

FOR  STUDENTS  AND  PRACTITIONERS 


BY 

HARRIS  E.  SANTEE,  A.  M.,  M.  D.,  Ph.  D. 

PROFESSOR    OF   NERVOUS    ANATOMY     IN    CHICAGO      COLLEGE    OF    MEDICINE     AND     SURGERY, 

MEDICAL     DEPARTMENT   OF  VALPARAISO   UNIVERSITY;  PROFESSOR  OF  ANATOMY     IN 

JENNER     MEDICAL     COLLEGE,     CHICAGO;     MEMBER     OF     ASSOCIATION      OF 

AMERICAN  ANATOMISTS.      FORMERLY  PROFESSOR   OF  ANATOMY   IN  THE 

COLLEGE  OF  PHYSICIANS  AND  SURGEONS,   CHICAGO,   MEDICAL 

DEPARTMENT  OF  THE   UNIVERSITY  OF     ILLINOIS;    AND 

PROFESSOR  OF    ANATOMY  IN  HARVEY  MEDICAL 

COLLEGE,   CHICAGO 


FIFTH  EDITION,  REVISED  AND    ENLARGED 

WITH    158    ILLUSTRATIONS,   46  OF  WHICH 

ARE  PRINTED  IN  COLORS 


PZ-^Oi 


PHILADELPHIA 

BLAKISTON'S  SON  &  CO. 

1012  WALNUT  STREET 


Copyright,  1915,  by  P.  Blaktston's  Son  &  Co. 


THE  MAPI.K  PRKSS  YORK  PA 


PREFACE 


The  recent  advances  in  human  anatomy  and  its  allied 
sciences  necessitate  the  thorough  revision  this  work  has 
received.  To  place  it  fairly  abreast  of  the  times  every 
section  has  been  largely  rewritten  in  accordance  with  the  dis- 
coveries of.  the  past  few  years.  Being  designed  for  a  text- 
book, the  subject-matter  is  presented  in  the  order  found  con- 
venient to  the  dissector.  The  description  proceeds  from  the 
gross  structures  to  the  constituent  neurones  in  each  successive 
region.  Wherever  the  embryology  will  assist  the  student  to 
comprehend  the  adult  forms,  the  development  is  briefly  given. 
The  embryology  is  more  fully  interwoven  with  the  regular  text 
than  in  the  fourth  edition;  and,  because  of  this,  the  special  em- 
bryologic  chapter  is  omitted.  All  other  chapters  are  elaborated 
and  illustrated  by  a  number  of  new  histologic  and  diagrammatic 
drawings;  they  are,  therefore,  somewhat  enlarged,  but  the 
author  has  kept  them  within  reasonable  bounds.  Some  ex- 
cellent illustrations  also  have  been  introduced  from  the  fifth 
edition  of  Morris's  ''Anatomy." 

The  special  objects  held  in  view  throughout  the  book  are  the 
location  of  functional  centers  and  the  tracing  of  their  afferent, 
associative  and  efferent  connections.  Particular  emphasis  is 
laid  upon  the  origin,  course,  termination  and  function  of  con- 
duction paths  as  they  are  met  in  the  regular  study,  and  the 
more  important  and  better  known  of  these  paths  are  summed 
up  in  a  final  chapter  on  the  tracing  of  impulses.  Function  is 
everywhere  correlated  with  structure;  and  so  far  as  present 
knowledge  permits,  the  function  of  each  group  of  neurones  is 
given  in  connection  with  its  anatomical  description. 

The  BNA  Nomenclature  is  followed  almost  without  excep- 
tion, the  English  equivalents  of  the  Latin  terms  being  very 
largely  employed.  Reason  and  experience  both  show  the  fun- 
damental value  of  the  Basle  Nomenclature  of  Anatomy.     Minor 


vi  PREFACE 

details  yet  remain  to  be  perfected;  but  the  elimination  of  proper 
nouns  and  the  adoption  of  correct  descriptive  names  for  all 
anatomic  structures  has  already  done  a  great  service  for 
science  and  been  of  vast  assistance  to  the  student.  In  the 
present  revision  the  compound  names  of  fiber-tracts  are  made 
more  descriptive  by  placing  first  that  element  of  the  noun 
which  represents  the  origin  of  the  tract  and  that  element  last 
which  indicates  the  termination  of  the  tract.  The  noun  is 
thus  given  added  pedagogic  value:  it  more  perfectly  expresses 
the  facts,  and  is  in  accord  with  the  descriptive  requirements  of 
the  BNA  Commission.  The  terms  '^ventral"  and  ^'dorsal" 
are  used  especially  to  designate  local  relation  and  direction 
within  the  individual  columns  of  the  spinal  cord. 

Keeping  pace  with  the  lectures,  every  student  is  expected  to 
dissect  the  human  brain  in  the  laboratory,  exposing,  studying 
and  sketching  every  macroscopic  structure  as  it  occurs  in  the 
work;  and,  then  with  the  microscope,  examine  the  minute 
structure  and  picture  the  histology  of  the  same  parts.  For 
these  purposes  the  class  should  be  taken  in  small  sections,  di- 
vided into  groups  of  two  to  four  students,  and  each  group  should 
be  provided  with  a  well-hardened  human  brain.  It  is  desirable 
that  each  student  should  receive  a  well-stained  microscopic 
section  of  every  important  part.  This  is,  however,  often 
impossible;  and  the  instructor  may  get  along  with  considerable 
satisfaction,  by  having  the  students  exchange,  if  he  has  but  a 
few  sets  of  slides. 

The  author  gratefully  acknowledges  the  courtesy  of  his 
publishers  in  allowing  the  use  of  illustrations  from  Gordinier's 
''Central  Nervous  System,"  Brubaker's  ''Physiology," 
McMurrich's  "Embryology,"  Morris's  "Anatomy,"  etc.,  and 
takes  this  opportunity  to  express  his  appreciation  of  the 
artistic  work  of  Dr.  Zan  D.  Klopper. 

Thankful  for  the  favor  and  kind  consideration  accorded 
to  former  editions,  both  in  our  own  country  and  in  England,  the 
author  hopes  that  the  present  work  may  receive  an  equally 
cordial  reception  and  prove  really  useful  to  many. 

Harris  E.  Santee. 


TABLE  OF  CONTENTS 

CHAPTER  I 
THE  MENINGES  OF  THE  BRAIN 

Page 

Their  Evolution i 

Dura  Mater  of  the  Brain: i-8 

Structure  and  relations i 

Processes 2 

Sinuses 3 

Arachnoid  granulations  (Pacchionii) 6 

Arteries 6 

Nerves 8 

Contrasted  with  dura  of  spinal  cord 8 

Arachnoid  of  the  Brain: 8-10 

Structure 9 

Relations,  subarachnoid  spaces 9 

Vessels  and  nerves 10 

Contrasted  with  arachnoid  of  the  cord 10 

Pia  Mater  of  the  Brain: 10-14 

Structure  and  relations 10 

Chorioid  tela  of  third  and  fourth  ventricles 11 

Chorioid  plexuses 11 

Cerebrospinal  fluid 12 

Arteries  and  veins      13 

Nerves 14 

Contrasted  with  pia  of  spinal  cord 14 

Blood  Supply  of  the  Brain: 14-28 

Carotid  and  vertebral  arteries 14 

A.  Cerebral  Circulation,  Arteries: 15 

Arterial  circle  (Willisi)  and  branches      .    •. 15 

Ai.  Cortical  system  of  arteries 16 

Anterior  cerebral  artery 16 

Middle  cerebral  artery 17 

Posterior  cerebral  artery 17 

vii 


Viii  CONTENTS 

Page 

Choroidal  arteries,  posterior  and  anterior     ....  i8 

A2.  Ganglionic  system  of  arteries 18 

Antero-median  ganglionic  arteries       20 

Antero-lateral  ganglionic  arteries 20 

Postero-median  ganglionic  arteries 20 

Postero-lateral  ganglionic  arteries 20 

The  Veins  of  the  Cerebrum: 20 

Internal  veins  of  the  cerebrum 21 

Great  vein  of  the  cerebrum  (Galeni) 21 

External  veins  of  the  cerebrum 22 

Superior 22 

Medial 22 

Inferior 22 

Lymphatics  of  cerebrum 23 

B.  Circulation  of  the  Rhombencephalon:      23-28 

Bi.  The  medulla  oblongata 23 

B2.  The  pons  (Varolii) 25 

B3.  The  cerebellum 26 

Superior  cerebellar  artery 27 

Anterior  inferior  cerebellar  artery 27 

Posterior  inferior  cerebellar  artery      27 

Internal  cerebellar  veins 28 

External  cerebellar  veins 28 

Superior 28 

Inferior 28 

Lymphatics  of  cerebellum 28 

Table  I.  Embryologic  Divisions  of  the  Brain: 28-29 

Components  of  cerebrum 29 

Components  of  rhombencephalon 30 

CHAPTER  II 

GENERAL  CONSIDERATION  OF  THE  BRAIN 

Neural  Plate  and  Tube 31 

Embryonic  Brain  Vesicles ^i 

Their  cavities — the  ventricles 33 

Superior  view ,, 

Posterior  view ^^ 

Inferior  view ^  - 

Anterior  area -  - 


CONTENTS  ix 

Middle  area ^ 

Posterior  area 

Roots  of  the  Twelve  Cerebral  Nerves: 39-47 

Nuclei,  genetic  and  terminal        30 

Olfactory  nerves .q 

Optic  nerve .  j. 

Oculo-motor  nerve .... 

4-^ 

Trochlear  nerve . , 

41 

Trigeminal  nerve .  j 

Abducent  nerve 42 

Facial  nerve .2 

Intermediate  nerve 42 

Acustic  nerve      42 

Glossopharyngeal  nerve 44 

Vagus  nerve 44 

Accessory  nerve 44 

Hypoglossal  nerve 47 

Brain  Measurements  and  Weights 47-50 

CHAPTER  m 
THE  CEREBRUM 


Physical  basis  of  mental  processes 51 

Subdivisions: 51-52 

End-brain 


51 

Inter-brain 51 

Mid-brain ^i 

Section  I.  The  Fore-brain  or  Prosencephalon:.    .    .  52 

Surface  of  fore-brain      53 

Definition  of  fissure  and  sulcus 53 

Subdivisions  and  borders 53 

Convex,  medial  and  basal  surface 53 

Fissures  and  sulci  of  convex  surface 54-58 

Longitudinal  fissure  of  cerebrum 54 

Transverse  fissure  of  cerebrum 54 

Lateral  fissure  of  cerebrum  (Sylvii) 55 

Sulcus  centralis  (Rolandi) 56 

Occipi to-parietal  sulcus ^.  57 

Lobes  and  gyri  of  convex  surface 58-71 

Frontal  lobe,  its  gyri  and  sulci 58 


CONTENTS 

Page 

Parietal  lobe,  its  gyri  and  sulci 6i 

Occipital  lobe,  its  gyri  and  sulci 65 

Temporal  lobe,  its  gyri  and  sulci 68 

Superior  surface 68 

External  surface 69 

Island  (Reili),  its  sulci  and  gyri 7° 

The  base  of  the  fore-brain 71-86 

Frontal  lobe,  inferior  surface 7  2 

Island  (Reili),  inferior  surface 73 

Rhinencephalon 73 

Olfactory  lobe 75 

Olfactory  bulb 75 

Olfactory  tract  and  striae 76 

Olfactory  triangle      7^ 

Parolfactory  area  (Brocae) 7^ 

Anterior  perforated  substance 79 

Tentorial  area  of  basal  surface 79-82 

Chorioidal  fissure 80 

Hippocampal  fissure 80 

Ectorhinal  sulcus 81 

Fissura  collateralis 81 

Inferior  temporal  sulcus 81 

Gyrus  fusiformis 81 

Gyrus  lingualis 81 

Limbic  lobe,  inferior  part 82 

Gyrus  hippocampi  and  uncus 82 

Dentate  fascia    .  " 82 

Hypothalamus 83-86 

Pars  optica  hypothalami 83-85 

Lamina  cinerea  terminalis 83 

Optic  chiasma,  nerves  and  tracts 83 

Tuber  cinereum  and  infundibulum 84 

Hypophysis  (pituitary  body) 85 

Pars  mammillaris  hypothalami 85-86 

Corpora  mammillaria 85 

Fissures  and  sulci  of  medial  and  tentorial  surface   .    .  86-92 

Sulcus  cinguli  (calloso-marginal) 87 

Subparietal  sulcus      87 

Callosal  sulcus 88 

Occipito-parietal  sulcus 89 


CONTENTS  ^■^SP   Xi 


Page 

Calcarine  fissure 89 

Hippocampal  fissure 91 

Chorioidal  fissure 91 

Collateral  fissure 92 

Ectorhinal  sulcus 92 

Inferior  temporal  sulcus 92 

Gyri  of  medial  and  tentorial  surface       92-98 

Gyrus  fornicatus 93 

Gyrus  cinguli 93 

Gyrus  hippocampi 93 

Uncus 94 

Lobus  pyriformis 94 

Limbic  lobe,  rhinencephalon 94-96 

Gyrus  rectus 96 

Gyrus  frontalis  superior  (g.  mlarginalis) 96 

Lobulus  paracentralis 96 

Prascuneus 96 

Cuneus 96 

Gyrus  lingualis 96 

Gyrus  fusiformis 97 

Summary  of  lobes  of  the  cerebrum 98 

Neopallium      98 

Rhinencephalon  (archipallium) 98 

Corpus  striatum 98 

Ventricles  and  gross  structures  of  the  fore-brain      .    .  98-140 

Internal  capsule     99-104 

Inferior  lamina 100 

Motor  fibers 100 

Sensory  fibers      100 

Superior  lamina      loi 

Genu,  frontal  and  occipital  parts 1 01-10  2 

Motor  fibers 102 

Common  sensory  fibers 103 

Special  sense  fibers 101-102 

Corpus  callosum:        104-108 

Upper  surface     io4 

Gyri  supracallosus  and  subcallosus 104-106 

Inferior  surface 106 

Borders,  posterior  and  anterior 106 

Splenium,  rostrum,  genu,  truncus 106 


Xii  CONTENTS 

Page 

Boundaries  of  general  cavity  of  fore-brain 107-108 

Body  of  fornix 108 

Crus  fornicis 10^ 

Columnae  fornicis lOQ 

Septum  pellucidum 109 

Fifth  ventricle no 

Lateral  ventricle  and  its  boundaries 111-127 

Central  part  (body) 113 

Corpus  striatum 113 

Lentiform  nucleus 1 14 

Nucleus  caudatus 116 

Stria  terminalis      117 

Thalamus 119 

Lamina  chorioidea  epithelialis 117 

Chorioid  plexus  of  lateral  ventricle 119 

Chorioid  glands 120 

Anterior  horn  of  the  lateral  ventricle 123 

Posterior  horn 123 

Inferior  horn 123 

Trigonum  collaterale ' 124 

Hippocampus,  its  digitations 125 

Chorioid  epithelium 126 

Third  Ventricle  and  Inter-brain      127-140 

Posterior  commissure 130 

Roof  epithelium 131 

Pineal  body 131 

Chorioid  tela  of  third  ventricle 132 

Anterior  commissure 133 

Lamina  terminalis 135 

Thalamus 136 

Extremities — anterior  and  posterior 137 

Surfaces — medial,  superior,  lateral  and  inferior  137 

Tegmental  hypothalamic  region 139 

Nucleus  hypothalamicus  (Luysi) 139 

Red  nucleus 139 

Lateral  geniculate  body 140 

Medial  geniculate  body 140 

Section  II.  The  Mid-brain  (Mesencephalon):    .    .    .   140-165 

Cerebral  peduncles  and  quadrigeminal  lamina  or  tectum  143 
Surfaces— superior,  inferior,  anterior,  posterior.    .    .    .   141-142 


CONTENTS  Xiii 

Page 

Bases  pedunculi 144 

Intermediate  bundle 145 

Temporo-pontal  tract 146 

Pyramidal  tract      145 

Fronto-pontal  tract 147 

Substantia  nigra 147 

Interpeduncular  nucleus 147 

Tegmenta i4y_i^p 

Cerebral  aqueduct  (Sylvii) 148 

Nuclei  of  oculo-motor  and  trochlear  nerves  ....  150 

Mesencephalic  nucleus  and  root  of  trigeminal  nerve  151 

Dorsal  longitudinal  bundle  of  Schiitz 151 

Formatio-reticularis 151 

Tegmental  decussations 152 

Tracts  of  fibers  in  the  tegmentum  .    .    .    .    .    .    .    .   152-164 

Medial  (or  posterior)  longitudinal  bundle .    ...  152 

Anterior  tecto-spinal  bundle 155 

Lateral  tecto-spinal  fasciculus      156 

Anterior  reticulo-spinal  fasciculus 154 

Lateral  reticulo-spinal  fasciculus 155 

Fillet  or  lemniscus 156 

Medial  fillet — superior  fillet 157 

Lateral  fillet 157 

Spino-thalamic  tract      159 

Brachium  conjunctivum 160 

Rubro-spinal  tract 161 

Thalamo-spinal  tract 161 

Thalamo-olivary  fasciculus       161 

Gustatory  tract 161 

Descending  root  of  trigeminal  nerve       162 

Quadrigeminal  lamina  or  tectum 164 

CoUiculus  superior 164 

Colliculus  inferior       164 

Brachium  superius 165 

Brachium  inferius 165 

Section  III.     Structure  of  the  Cerebrum:      ....  165 

The  neurone  or  nerve  cell 167 

Origin  and  development  of  neurones 167 

Classification  of  neurones 167 

Multipolar  neurones 169 


Xiv  CONTENTS 

Page 

Types  I  and  II 171 

Bipolar  neurones 17S 

Fusiform  and  pear-shaped 175-176 

Cell-bodies  or  neurone  centers 169^175 

Axones 171,176,177 

Dendrites i74,  '^l^y  ^77 

Neurone  doctrine 178 

Myelin  sheath 178 

Orders  of  neurones  (ist,  2d,  etc.) 179 

Functions  of  neurones 179 

Degeneration  of  neurones 180 

Regeneration  of  neurones 180 

Sustentacular  tissue 182 

Epiblastic 182 

Ependyma  and  Neuroglia 182 

Mesoblastic  connective  tissue 183 

Groups  of  neurones 183 

Ganglia 183 

Nuclei 183 

Nerves,  fasciculi,  funiculi 184 

Neurone  cycles  or  reflex  arcs 184 

Synapses     186 

Cortical  gray  matter 186 

Thickness,  area,  mass,  specific  gravity 188 

Types  of  cortex      188 

Cortical  or  cerebral  localization 189-216 

Motor  area,  emissive 189 

Psychic  motor  area 190 

Common  sensory  area 190 

Psychic  sensory  area 190 

Acustic  center iqi 

Optic  center 1^2 

Olfactory  and  gustatory  centers 192 

Nammg  center 1^2 

Centers  of  intonation,   equilibration   and  orienta- 
tion   192 

Anterior  association  center  of  abstract  conceptions  .  193 

Posterior  association  center  of  concrete  conceptions .  194 

Middle  association  center 104 

Cell  and  fiber  lamination 195-216 


CONTENTS  XV 

Page 

Plexiform  layer 196-198 

Layer  of  small  pyramids 196  and  198 

Layer  of  medium-sized  pyramids 196  and  200 

External  layer  of  large  pyramids 196  and  200 

Layer  of  stellate  cells 196  and  201 

Internal  layer  of  large  pyramids 196  and  201 

Layer  of  fusiform  cells 196  and  202 

Atypical  neurones 202 

Systems  of  cortical  axones 204 

Radiations  of  Meynert 204 

Association  fibers  of  Meynert 204 

Atypical  cortex 204-213 

Visual  cortex 204 

Olfactory  cortex 205 

Olfactory  bulb 205 

Uncus  hippocampi 207 

Nucleus  amygdalae 209 

Subiculum 209 

Fascia  dentata 211 

Trigonum  olfactorium,  etc 211 

Gyrus  cinguli ,  .    .  212 

Claustrum 213 

Histogenesis  of  cerebral  cortex    .........  213 

Three  cell-layers,  two  fiber-layers  (J.  S.  Bolton)  .  213 

Visceral,  somatic,  and  association  areas 215 

Ganglionar  gray  matter 216-235 

Corpus  striatum 217 

Internuncial  fibers 218 

Centrifugal  fibers  or  strio-fugal  fibers 218 

Centripetal  fibers  or  strio-petal  fibers 219 

Thalamus 220 

Thalamic  nuclei 221 

Metathalamus 228 

Optic  and  acustic  radiations 228-229 

Red  nucleus 229 

Nucleus  hypothalamicus 232 

Superior  coUiculi  of  corpora  quadrigemina    ....  232 

Tecto-spinal  and  tecto-cerebellar  tracts 233 

Inferior  coUiculi  of  corpora  quadrigemina     ....  234 

Nucleus  lateralis  superior  (tegmenti  profundus)  .    .  235 

Anterior  and  lateral  reticulo-spinal  tracts     ...  235 


Xvi  CONTENTS 

Page 

Substantia  nigra 235 

Central  or  ventricular  gray  matter 235-239 

Hypothalamus 235 

Pars  optica      235 

Pars  mammillaris 236 

Massa  intermedia  (middle  commissure) 237 

Stratum  griseum  centrale  of  mid-brain 237 

Dorsal  tegmental  nucleus 237 

Oculomotor  nucleus 238 

Trochlear  nucleus 238 

Trigeminal  nucleus  of  mid-brain 239 

Projection  fibers  of  the  cerebrum 240-251 

Corticifugal,  or  motor  fibers 240-246 

Strio-fugal  tracts 241 

Intermediate  path 241 

Fronto-pontal  tract 241 

Temporo-pontal  tract 241 

Pyramidal  tract 242 

Head  and  neck  fibers 244 

Upper  extremity  fibers      244 

Trunk  fibers 244 

Lower  extremity  fibers 244 

Destruction  of  by  clot,  etc 246 

Sensory  or  corticipetal  fibers 246-251 

Medial  fillet,  spino-thalamic  tract  and  brachium 

conjunctivum 247 

Olfactory  projection  fibers 247-249 

Cortical  fillet  (common  sensory) 249-250 

Taste  fibers 250 

Auditory      2:;o 

Lateral  fillet  and  brachium  inferius 250 

Temporo- thalamic  radiation 250 

Occipito- thalamic  radiation  (optic) 250 

Commissural  fibers  of  cerebrum 251-253 

Corpus  callosum 251 

Anterior  commissure 21:2 

Commissura  hippocampi      2=;^ 

Association  fibers  of  cerebrum 253-260 

Short  association  fibers 2^^ 

Long  association  fibers 255-260 


CONTENTS  xvii 

Page 

Cingulum  of  gyrus  fornicatus 255 

Fornix 256 

Uncinate  fasciculus 257 

Superior  longitudinal  fasciculus       259 

Inferior  longitudinal  fasciculus 257 

Fasciculus  occipito-fron talis  superior  and  inferior  259 

Perpendicular  fasciculus 260 

Fore-brain  adapted  to  psychic  function 260 

Evolution  of  brain 260-261 

CHAPTER  IV 
THE  RHOMBENCEPHALON 

Section  I.    The  Cerebellum: 262-292 

Origin 262 

Function      263 

Divisions:        263 

Cerebellar  hemispheres 263 

Vermis  cerebelli  or  worm      263 

Cerebellar  notches,  anterior  and  posterior 264 

Medullary  Body: 265 

Inferior  medullary  velum 265 

Brachia  conjunctiva 263 

Superior  medullary  velum  (Vieussensi) 266 

Corpora  restiformia 267 

Brachia  pontis 267 

Horizontal  sulcus  of  cerebellum      268 

Superior  Surface  of  Cerebellum: 269-273 

Sulci  of  upper  surface 269-271 

Precentral  sulcus 269 

Post-central  sulcus 269 

Predeclivil  sulcus 269 

Post-declivil  sulcus 271 

Lobes  of  superior  surface 271 

Lobus  lingulae 271 

Lobus  centralis 272 

Lobus  culminis  monticuli      272 

Lobus  declivis  monticuli 272 

Lobus  folii  vermis 273 

Inferior  Surface  of  Cerebellum: 273-278 


xviii  CONTENTS 

Page 

Sulci  of  lower  surface 273-275 

Post-nodular  sulcus 273 

Prepyramidal  sulcus 274 

Post-pyramidal  sulcus 274 

Midgracile  and  post-gracile 274 

Lobes  of  lower  surface 275-277 

Lobus  noduli 275 

Lobus  uvulae 276 

Lobus  pyramidis 276 

Lobus  tuberis      276 

Cortical  Gray  Matter  of  the  Cerebellum 278-284 

Superficial  layer 278 

Stratum  cinereum 278 

Stratum  gangliosum 278-279 

Cells  of  Purkinje  and  stellate  cells 278-279 

Fibers  of  superficial  layer 279 

Deep  layer  (stratum  granulosum) ;  280 

Cells  of  granular  layer      280 

Fibers  of  granular  layer 282 

Function  of  stellate,  granule  and  Purkinje  cells  282 

Neuroglia  of  cerebellum 282 

Histogenesis 282-283 

Ganglionar  Gray  Matter  of  Cerebellum,  the  Nuclei .    .    .    .  284-287 

Function,  relay  stations 284 

Nucleus  dentatus 284 

Nn.  emboliformis,  globosus  and  fastigii 285-286 

White  Substance — Corpus  Medullare: 286-290 

Projection  fibers 287-290 

Brachium  conjunctivum 287 

Superior  medullary  velum 287 

Brachium  pontis 288 

Corpus  restiforme 289 

Commissural  fibers 290 

Association  fibers 290 

Section  IL    The  Pons  (Varolii)  : 292-316 

Surfaces:      29^ 

Superior  and  inferior 293 

Anterior  (Tuber  annulare) 293 

Posterior— ventricular,  and  attached  part     ....  293-295 

Transverse  fibers  of  the  pons 295-297 


CONTENTS  XIX 

Page 

Superficial  of  pars  basilaris  pontis      295 

Deep  transverse  of  pars  basilaris  pontis 296 

Transverse  of  pars  dorsalis  pontis 296 

Trapezoid  body 296 

Longitudinal  fibers  of  the  pons 296-305 

Basilar 295 

Dorsal 295-305 

Medial  fillet  and  superior  fillet 298 

Lateral  fillet 299 

Spino-thalamic   tract 299 

Spino-tectal  tract 300 

Ventral  spino-cerebellar  tract 300 

Medial  longitudinal  bundle 301 

Gustatory  tract 302 

Spinal  tract  of  the  trigeminal  nerve 302 

Mesencephalic  root  of  the  trigeminal  nerve  .    .    .  302 

Tecto-spinal  fasciculi 303 

Reticulo-spinal  fasciculi 303 

Thalamo-olivary  and  thalamo-spinal  tracts  .    .    .  304 

Rubro-spinal  tract 304 

Dorsal  longitudinal  bundle  of  Schiitz 305 

Gray  Matter  of  the  pons  . 305-316 

Nucleus  pontis V   .    .    .    .  305 

Origin 306 

Gray  Matter  of  pars  dorsalis 307-316 

Superior  olivary  nucleus 307 

N.  praeolivaris  and  n.  semilunaris 307 

Nucleus  of  trapezoid  body 308 

Nuclei  of  recticular  formation 309 

Reticulo-spinal  tracts  (CoUieri) 309 

Nuclei  of  trigeminal  nerve 309 

Genetic  (motor)      309 

Terminal  (sensory) 311 

Nucleus  of  abducent  nerve 312 

Nucleus  of  facial  nerve 313 

Salivary  nucleus 314 

Vestibular  nucleus  of  auditory 315 

Lesions  in  pons 315 

Section  III.    Medulla  Oblongata  (Myelencephalon)  :  316-355 

Origin 3^7 


XX  CONTENTS 

Page 

Ventricle 3i8 

Surfaces 318-323 

Anterior  lateral  sulcus 3^^ 

Posterior  lateral  sulcus      3^8 

Anterior  surface 3^9 

Lateral  surface 320 

Olive 320 

Lateral  column 320 

Posterior  surface 320 

Restiform  body 321 

Roof  epithelium  of  fourth  ventricle 322 

Floor  of  fourth  ventricle 323 

White  matter  of  medulla 323-338 

Substantia  reticularis 324 

Raphe 324 

Transverse  fibers 324 

Pyramidal  decussation 325 

Fillet  decussation 325 

Olivo-cerebellar  fibers 325 

Arcuate  fibers,  external  and  internal 325 

» Dorso- ventral  fibers 326 

Anterior  external  arcuate 326 

Roots  of  eighth  to  twelfth  cerebral  nerves     ...  326 

Longitudinal  fibers  of  anterior  area: 326-331 

Pyramid,  anterior  and  lateral  tracts 327 

Medial  fillet  (interolivary  stage) 329 

Medial  longitudinal  bundle  (posterior) 330 

Anterior  tec  to-spinal  bundle 331 

Longitudinal  fibers  of  lateral  area       332-334 

Fasciculus  lateralis  proprius 332 

Vestibulo-spinal  tract 332 

Ventral  spino-cerebellar  tract 333 

Spino-thalamic  tract 333 

Rubro-spinal  tract 333 

Longitudinal  fibers  of  posterior  area 334-338 

Funiculus  gracilis 33^ 

Funiculus  cuneatus 33r 

Spinal  tract  of  trigeminal  nerve 335 

Dorsal  spino-cerebellar  tract 336 

Restiform  body 335 


CONTENTS  '^g^am'      XXI 


Page 

Vestibular  and  cochlear  nuclei 336 

Ponto-bulbar  nucleus 337 

Tractus  solitarius 338 

Gray  matter  of  the  medulla 338-356 

Nucleus  of  external  arcuate  fibers 339 

Origin 339 

Nuclei  in  floor  of  ventricle  (s.  nucleare) 339 

Hypoglossal  nucleus 341 

Nucleus  lateralis  inferior 341 

Nucleus  ambiguus 341 

Nuclei  alae  cincereae 342 

Nucleus  cardiacus .   * 342 

Nucleus  salivarius 344 

Nucleus  tractus  solitarii 345 

Nucleus  tractus  spinalis  n.  trigemini 346 

Vestibular  nuclei 348 

Cochlear  nuclei 350 

Special  nuclei  in  medulla 351 

Nucleus  funiculi  gracilis 351 

Nucleus  funiculi  cuneati 353 

Nucleus  olivaris  inferior 354 

Origin 355 

Section  IV.    The  Fourth  Ventricle: 356-371 

Boundaries 358 

Floor  of  fourth  ventricle 358 

Colliculus  facialis 359 

Fovea  superior 359 

Locus  caeruleus 359 

Hypoglossal  triangle      360 

Ala  cinerea  (trigonum  vagi) 360 

Area  acustica 360 

Origin  of  cerebral  nerves      361-371 

Table  II.  Sensory  Nerves  and  Roots 363 

Table  III.  Motor  Nerves  and  Roots      364 

Nervus  terminalis 365 

Terminal  nuclei 365 

Somatic  and  visceral 365 

Common  sensory 366 

Cortical  and  reflex  connections 366 

Special  sense 367 


XXU  CONTENTS 

Page 

Cortical  and  reflex  connections 368 

Optic  and  olfactory  nuclei 368-369 

Genetic  nuclei 37° 

Somatic  and  visceral 37^ 

Cortical  and  reflex  connections 37 1 

CHAPTER  V 

MEMBRANES  OF  THE  SPINAL  CORD 

Dura  mater 372 

Arachnoid '    *    '  '^^^ 

Lumbar  puncture 374 

Pia  mater 375 

Blood  Supply  of  the  Spinal  Cord: 376-378 

Spinal  arteries,  anterior  and  posterior 376 

Fissural  or  centrifugal ••  377 

Centripetal      377 

Venae  spinales  internae 378 

Root  and  fissural  veins 378 

Venae  spinales  externae 378 

Internal  vertebral  plexus 378 

L)anphatics 378 

CHAPTER  VI 

THE  SPINAL  CORD 

Extent 379 

Diameters 379 

Cervical  enlargement 380 

Lumbar  enlargement 382 

Ventricle  (canalis  centralis  spinalis) 382 

Fissures  of  the  cord:      382 

Anterior  median  Assure 382 

Posterior  median  fissure 382 

Posterior  lateral  sulcus 385 

Anterior  root-line  (s.  lateralis  anterior)      387 

Posterior  intermediate  sulcus 387 

I.  Gray  Matter  of  the  Cord: 387-402 

H-shaped  column 388 

Four  functional  columns 38S 


CONTENTS  xxiii 

Page 

Substantia  gelatinosa 388 

Substantia  spongiosa 388 

Gray  crescent     . 388 

Anterior  columna 389 

Cells  of  anterior  columna 389 

Golgi  cells -. 389 

Deiters  cells 389 

Medial  column 389 

Lateral  column 389 

Cortical  connection 392 

Reflex  mechanism 393 

Lesions  of  anterior  columna 393 

Center  of  crescent  and  columna  lateralis 394~395 

Intermedio-lateral  column  of  cell-bodies  (efferent 

sympathetic  neurones) 394 

Posterior  columna      395 

Substantia  gelatinosa 396 

Neurones  of  head  of  posterior  columna     ....  396 
Nucleus  dorsalis  (Clarki)  terminal  nucleus  of  sym- 
pathetic)    398 

Gray  commissure  of  spinal  cord 400 

Gray  anterior  commissure 400 

Posterior  commissure 400 

Lesions  of  gray  substance 401 

2.  White  Matter  of  the  Spinal  Cord: 402-426 

Transverse  fibers 402 

White  anterior  commissure 402 

Dorso-ventral  fibers 403 

Longitudinal  fibers        403 

Funiculus  anterior 403 

Funiculus  lateralis 404 

Funiculus  posterior 404 

Embryological  method  of  locating  tracts 404 

Pathological  and  experimental  method 405 

Tracts  of  the  Spinal  Cord 405-418 

Anterolateral  fasciculus  proprius 405 

Medial  longitudinal  bundle 406 

Anterior  pyramidal  tract 407 

Anterior  tecto-spinal  bundle 407 

Vestibulo-spinal  tract 408 


Xxiv  CONTENTS 

Page 

Gowers's  tract 409 

Spino-reticular  tract 409 

Spino-tectal  tract 410 

Ventral  spino-cerebellar  tract 410 

Spino-thalamic  tract 410 

Spino-olivary  tract  (Triangular  tr.  of  Helwig).    .  411 

Dorsal  spino-cerebellar  tract  (Tract  of  Flechsig) .    .  411 

Spino-vestibular  tract 412 

Lateral  pyramidal  tract 412 

Rubro-spinal  and  thalamo-spinal  tract 413 

Lesions  of  anterior  and  lateral  funiculi      413 

Marginal  tract  (Lissaueri) 414 

Posterior  funiculus 415 

Functions  of  posterior  funiculus 415-416 

Entry  zone 415 

Fasciculus  gracilis  (GoUi) 416 

Fasciculus  cuneatus  (Burdachi)       .........  417 

Descending  tracts  from  posterior  roots 417 

Descending  postero-medial  tract  (comma,  oval, 

septo-marginal  and  median  triangular  tract)  .  417 

Descending  posterolateral  tract 418 

Posterior  fasciculus  proprius 418 

Comu-commissural  tract 418 

Lesions  of  posterior  columns 418 

Roots  of  the  spinal  nerves 418-426 

Anterior  root 410 

Point  of  exit 410 

Real  origin  (genetic  nuclei) 41  p 

Voluntary  motor  fibers 410 

Sympathetic  efferent  fibers      4ip 

Lesions ...« 

419 

Posterior  root .20 

Spinal  ganglion  (origin) 420-421 

Point  of  entrance  into  the  cord 420 

Real  central  termination,  and  terminal  nuclei  ...  420 

Gray  matter  of  the  cord 420 

Nuclei  of  medulla  oblongata 421 

Physiological  groups  of  posterior  root-fibers      ...  423 

Lesions  of  posterior  roots      424 

Four  systems  of  fibers  in  common  afferent  nerves  424-426 


CONTENTS  XXV 

Page 

Proprio-ceptors 424 

Protopathic  extero-ceptors 425 

Epicritic  extero-ceptors 425 

Intero-ceptors 426 

The  law  of  their  conduction  in  combinations.  .  426 

Law  of  integration 426 

CHAPTER  VII 

TRACING  OF  IMPULSES 

Rate  of  nerve  impulses 427 

I.  Efferent,  or  Motor  Paths: 427-436 

Cerebrospinal  or  pyramidal  paths      .........   427-430 

Through  spinal  nerves .  429 

Through  cerebral  nerves 429 

Cerebropontal  paths 430-432 

Fronto-pontal 430 

T.emporo-pontal 430 

Intermediate 430 

Spinal  and  cerebral 430 

Paths  through  red  nucleus 432 

Rubro-spinal  path,  direct 432 

Paths  through  the  thalamus 433 

Reticulo-spinal  paths  (Collieri) 433 

Anterior  reticulo-spinal  tract ,  433 

Lateral  reticulo-spinal  tract 433 ' 

Short  fiber  paths  in  formatio-reticularis 433 

II.  Afferent,  or  Sensory  Paths,  General  Sensations:    .    .    .   436-441 

Tactile,  muscular,  pain,  and  temperature  sense   .    .    .  436-441 
(I).  Muscular  and  tactile  impulses  from  muscles,  skin, 

etc 436 

Through  fasciculi  gracilis  et  cuneati 436 

Direct  route 437 

Indirect  route 437 

Through  cerebral  nerves  and  medial  fillet 439 

(II).  Paths  for  pain,  temperature  and  tactile  impulses  439 

Through  spino- thalamic  tract      439 

Through  ventral  spino-cerebellar  tract      439 

Through  cerebral  nerves  and  spino- thalamic  tract  440 

Short  fiber  paths 440 


XXvi  CONTENTS 

Page 

Afferent  Paths — Special  Sensations: 441-447 

Olfactory  path 44i 

Optic  path 443 

Auditory  path 445 

Cochlear  (hearing  proper) 445 

Vestibular  (equilibrium)       445 

Reflex  connections 446 

Gustatory  path      446 

Lesions  of  special  sense  paths .    447 

III.  Reflex  Paths:      447-460 

Reflex  arcs 448 

(i)  Spinal  reflexes      448 

Defecation  reflexes 448 

(2)  Cerebral  reflexes      449 

(3)  Spino-cerebral  reflexes 452 

With  centers  in  the  red  nucleus      452 

In  the  thalamus 452 

In  quadrigeminal  coUiculi 45  2 

In  lentiform  nucleus 452 

(4)  Cerebrospinal  reflexes 452 

Respiratory  reflexes 452 

Equihbrium  reflexes       453 

Pupillary  reflexes 4^4 

(5)  Cerebellar  reflexes       45  c 

Through  ventral  spino-cerebellar  tract      ....  455 

Swimming  reflexes 4^6 

Posture  reflexes 4^7 

Stepping  reflexes 4^8 

Reflex  educated  movements 450 

Visceral  paths   to    the   cerebellum,  spinal   and 

cranial 4^p 

Dorsal  spino-cerebellar  tract 459 

Nucleo-cerebellar  fibers 460 

INOEX 46J 


LIST  OF  ILLUSTRATIONS 


Fig.  Page 

1.  Sagittal  section  of  skull,  showing  falx  cerebri,  falx  cerebelli, 

a  part  of  the  tentorium  cerebelli  and  the  sinuses  of  the 
dura  mater.     (After  Morrises  Anatomy) • .       3 

2.  Upper  surface  of  tentorium  cerebelli,  tentorial  notch  and 

certain  sinuses  of  the  dura.     (After  Morris's  Anatomy)  .       4 

3.  Sinuses  of  the  dura  mater  in  the  base  of  cranium,  etc. 

(After  Morrises  Anatomy) 5 

4.  Coronal  section  of  meninges  showing  falx  cerebri,  superior 

sagittal  sinus  and  the  arachnoid  granulations.     {Gor- 
dinier  after  Key  and  Retzius) 7 

5.  Middle  meningeal  artery  inside  the  cranium.     (After  Mor- 

ris's Anatomy) 8 

6.  Diagram  of  pia  mater  and  arachnoid,  showing  subarach- 

noid spaces.     (After  Morris's  Anatomy) 10 

7.  Horizontal  section  of  the  cerebrum.     Fornix  turned  back 

to  show  the  chorioid  tela  of  third  ventricle.     {Original)  .     12 

8.  Roof  and  lateral  walls  of  fourth  ventricle  and  its  chorioid 

plexus.     (After  Morris's  Anatomy) 13 

9.  Arterial  circle  of  Willis  and  its  branches.     The  base  of  the 

brain.     (After  Morris's  Anatomy) 15 

10.  Arterial  circle  (Willisi)  and  base  of  the  cerebrum.     (After 

Gordinier  from  Quain) 19 

11.  Middle  cerebral  artery,  and  its  branches.     (After  Gordi- 

nier from  Quain) 21 

12.  Anterior  and  posterior  cerebral  arteries.     (Aitei  Spalteholz)  24 

13.  Arteries  of  the  medulla  oblongata.     (Gordinier  after  Buret)  25 

14.  Median  section  of  embryonic  brain  of  third  month.     (After 

McMurrich  from  His)  . 26 

15.  Divisions  of  the  brain,  diagrammatic.     {AitQv  Morris's 

Anatomy) 30 

16.  Neural  tube  and  brain  vesicles.    A.  B.  C.  D.  andE.  (After 

Morris's  Anatomy) 34 

17.  Diagrammatic  horizontal  section  of  vertebrate  brain,  show- 

ing vesicles  and  ventricles.     (After  Morris  from  Huxley)     35 
xxvii 


Xxviii  I'IST   OF  ILLUSTRATIONS 

Fig.  .        ^^^^ 

1 8.  Diagrammatic  median  section  of  vertebrate  brain  showing 

vesicles,  ventricles  and  olfactory  diverticulum.     (After 

Morris  from  Huxley) • 3^ 

19.  Antero-superior  view  of  the  brain.     (Original)    .....  38 

20.  The  posterior  aspect  of  the  brain.     (Original) 40 

21.  The  base  of  bram.     (Original) 43 

22.  Convex  surface  of  left  cerebral  hemisphere  of  the  black 

monkey  (Macacus  maurus).     (Original) 45 

23.  The  island  of  Reil  in  right  hemisphere  of  the  black  monkey 

(Macacus  maurus).     (Original) 45 

24.  Medial  surface  of  right  hemisphere   of  black   monkey 

(Macacus  maurus).     (Original) 46 

25.  Base  of  fore-brain  from  black  monkey  (Macacus  maurus). 

(Original) 46 

26.  Latero-superior  aspect  of  the  brain,  showing  great  fissures, 

lobes,  poles  and  borders.     (Original) 55 

27.  The  convex  surface  of  the  cerebrum,  showing  the  fissures 

and  sulci.     (Original) 57 

28.  Gyri  of  the  convex  surface  of  the  cerebrum.     (Original)   .  60 

29.  Gyri  of  convex  surface  of  cerebral  hemisphere  in  outline  .  63 

30.  Lateral  aspect  of  the  brain.    Part  of  frontal  and  parietal 

lobes  are  cut  away  to  show  the  island  (Reili)  and  the 
superior  surface  of  the  temporal  lobe,  arachnoid  granula- 
tions, etc.     (Original) 64 

3 1 .  Base  of  the  fore-brain  and  cut  surface  of  mid-brain.     Right 

temporal  pole  is  cut  away.     (Original) 74 

32.  Gyri  on  base  of  fore-brain  in  outline 77 

33.  The  median  section  of  the  brain.     (Original) 88 

34.  Medial  surface  of  left  cerebral  hemisphere,  showing  lobes 

and  sulci.     (Original) 90 

35.  Gyri  on  medial  surface  of  hemisphere.     (Original).    ...  95 

36.  Gyri  of  medial  surface  of  cerebral  hemisphere  in  outline  .  97 

37.  Transverse  section  of  the  brain,  directed  from  the  pons  ob- 

liquely upward  and  forward,  showing  internal  capsule, 
corpus  callosum,  ganglia  and  ventricles  of  the  fore- 
brain.     (Original) loi 

38.  Horizontal  section  of  right  cerebral  hemisphere  cutting  cor- 

pus callosum,  internal  capsule,  corpus  striatum,  thala- 
mus, and  the  island.     (Original) 105 

39.  Sagittal  section  of  basal  part  of  right  cerebral  hemisphere 


LIST   OF  ILLUSTRATIONS  XXIX 

Fig.  Pagb 

showing  inferior  lamina  of  internal  capsule,  hippocam- 
pus, inferior  horn  of  lateral  ventricle.     (Original)   .    .    .   112 

40.  Diagram  of  internal  capsule  in  colors.     (Original)  .   .    .    .113 

41.  Brain-stem  viewed  from  the  left  side;  internal  capsule  in 

colors — red  tracts  are  descending,  blue  are  common 
ascending,  and  purple  are  special  ascending  (gustatory, 
optic  and  acustic).     (Original) ' 115 

42.  Dorsal  surface  of  corpus  callosum,  cerebral  hemisphere  cut 

away  to  expose  it.     (Original) 116 

43.  Fasciola  cinerea,  gyrus  subsplenialis  (Retzii)  and  fascia 

dentata,  longitudinal  and  transverse  parts.     (Original.)    118 

44.  Coronal  section  of  brain  through  red  nucleus,  showing  third 

ventricle  and  body  and  inferior  horn  of  lateral  ventricle. 
(After  Morrises  Anatomy) 120 

45.  The  inferior  and  posterior  horns  of  the  lateral  ventricle, 

shown  by  removal  of  their  lateral  walls.     (Original)   .    .   121 

46.  Horizontal  section  of  cerebrum,  cutting  splenium  and  genu 

of  corpus  callosum,  showing  lateral  ventricles,  septum 
pellucidum,  fornix  and  transverse  temporal  gyri. 
(Original) 122 

47.  Horizontal  section  of  cerebrum  just  below  splenium  of  cor- 

pus callosum,  showing  commissura  hippocampi,  fornix, 
septum  pellucidum,  the  island  and  lateral  ventricles. 
(Original) 125 

48.  Horizontal    section   of    cerebrum.     Fornix    turned   back 

showing  chorioid  tela  of  third  ventricle,  and  internal  cere- 
bral veins.     (Original) 128 

49.  Transverse  section  of  left  cerebral  hemisphere  cutting  the 

splenium  and  showing  the  posterior  horn  and  the  floor 

of  the  inferior  horn  of  the  lateral  ventricle.     (Original)   .  129 

50.  Horizontal  section  of  cerebrum  through  genu  and  below 

splenium  of  corpus  callosum,  fornix  and  chorioid  tela 
turned  back,  to  show  inter-brain  and  third  ventricle. 
(Original) 134 

51.  Dorsal  view  of  the  fornix.    Diagrammatic.    (Aiter  Morris's 

Anatomy) 135 

52.  Lateral  view  of  the  fornix.     Diagrammatic.    (Aitei Morris's 

Anatomy) 136 

53.  Lateral  and  dorsal  view  of  the  ventricles.     Diagrammatic. 

(Original) 138 


XXX 


LIST   OF  ILLUSTRATIONS 


Fig.  ^^°^ 

54.  Transverse  section  of  brain,  cutting  corpora  mammillaria. 

(After  Toldt,  Morris's  Anatomy) 142 

55.  The  region  of  the  mid-brain  showing  pulvinar  of  the  thala- 

mus, the  geniculate  bodies,  the  corpora  quadrigemina 
and  brachia,  the  pineal  body,  the  optic  tract  and  the 
fourth  nerve.     (Original) i44 

56.  The  dorsal  or  posterior  aspect  of  the  inter-brain,  the  mid- 

brain, the  pons  and  the  medulla.     (Original).    .    .    .    .    145 

57.  Anterior   aspect  of  the  mid-brain,  pons,   and  medulla. 

(Original) I49 

58.  Transverse  section  through  the  corpora  mammillaria  and 

the  superior  coUiculi  of  the  corpora  quadrigemina. 
(Original) i53 

59.  Section  of  the  mid-brain  through  superior  colliculi  and  the 

apparent  origin  of  the  oculo-motor  nerve.     (Original)   .    156 

60.  Section  of  the  mid-brain  cutting  the  inferior  colliculi  of  the 

corpora  quadrigemina.     (Original) 158 

61.  Stained  section  of  mid-brain   cut   through  the  superior 

colliculi.  White  substance  is  stained  black;  gray  sub- 
stance is  light.     (Original) 159 

62.  Stained  section  of  mid-brain  cut  through  inferior  colliculi. 

White  matter  stained  black;  gray  matter  is  light. 
(Original) 160 

63.  Diagrammatic  section  of  the  mid-brain  through  the  supe- 

rior colliculi.  Descending  tracts  in  red;  ascending  in 
blue.     (Original) 162 

64.  Diagrammatic  section  of  mid-brain  through  inferior  col- 

liculi. Descending  tracts  in  red;  ascending  tracts  in  blue. 
(Original) 163 

65.  Varieties  of  neurones  in  the  human  nervous  system.  (After 

Morris's  Anatomy) 166 

66.  Afferent  and  efferent  neurones,   showing  abundance  of 

tigroid  substance  in  resting  state  and  intracapsular  ac- 
cessory processes  of  the  afferent  neurone.  (After 
Morris's  Anatomy) 168 

67.  A  pyramidal  cell  of  the  cerebral  cortex  and  a  spinal  gang- 

lion cell  stained  to  show  neuro-fibrillae.  (After  Morris's 
Anatomy) i58 

68.  Motor  neurone.     (After  Barker's  Nervous  System) ....    170 


LIST    OP   ILLUSTRATIONS  XXXI 

Fig.  Page 

69.  An  efferent  neurone  and  an  afferent  neurone.     (After  Bru- 

baker^s  Physiology) 172 

70.  Medullated  and  non-medullated  axones.     A.  From  a  cra- 

nial or  spinal  nerve;  showing  nodes  of  Ranvier  and 
neurolemma.  B.  From  the  spinal  cord;  showing  unseg- 
mented  medullary  sheath  and  absence  of  neurolemma. 
C.  Sympathetic  fibers  possessing  neurolemma  both 
without  and  with  a  medullary  sheath.  (After  Morrises 
Anatomy) 173 

71.  Diagram  showing  development  of  neurones  in  the  spinal 

cord.     (McMurrich  after  S chaffer) 174 

72.  Illustrating  functions  of  neurones:  Afferent,  associative 

and  efferent.     (After  Morrises  Anatomy) 179 

73.  Neuroglia  cells  and  ependyma  cells  of  the  spinal  cord. 

(After  Lenhossekj  Gordinier's  Nervous  System) 181 

74.  Cortical  areas  on  convex  surface  of  cerebral  hemisphere. 

(Original) 187 

75.  Cortical  areas  on  the  medial  and  tentorial  surface  of  the. 

cerebral  hemisphere.     {Original) 191 

76.  Cortical  areas  after  C.  K.  Mills.     Convex  surface  of  cere- 

bral hemisphere.     {Brubaker's  Physiology) 193 

77.  Cortical  areas  after  C.  K.  Mills.     Medial  and  tentorial  sur- 

face of  cerebral  hemisphere.     (Brubaker's  Physiology)   .    194 

78.  Functional  regions  of  cerebral  cortex  on  the  convex  surface 

of  the  hemisphere  as  mapped  out  by  their  order  of  myel- 
inization.     (Aiter  Paul  Flechsig) 195 

79.  Functional  regions  of  cerebral  cortex  on  the  medial  sur- 

face of  a  hemisphere,  mapped  according  to  the  order  of 
their  medullation.     (After  Paul  Flechsig) 196 

80.  Cell-layers  and  fiber  zones  in  superior  parietal  lobule.    Dia- 

grammatic.    (Original) 197 

81.  Cell  and  fiber  lamination  in  the  posterior  half  of  the  ante- 

rior central  gyrus.     The  motor  area.     (After  A.   W. 
Campbell) 199 

82.  Cell  and  fiber  lamination  in  the  anterior  half  of  the  poste- 

rior central  gyrus.  '  The  common  sensory  area.     (After 

A.  W.  Campbell) 203 

Ss*  Cell  and  fiber  lamination  in  the  calcarine  region.     Recep- 
tive visual  area.     (After  A.  W.  Campbell) 206 


Xxxii  I-IST   OF   ILLUSTRATIONS 

Fig.  Page 

84.  Cell  and  fiber  lamination  in  the  uncus  hippocampi  (lobus 

pyriformis).  The  area  of  smell.  (After  A.  W.  Camp- 
bell)   208 

85.  Transverse  section  of  the  hippocampal  region.     (After 

Edinger) 210 

86.  Chief  elements  of  the  olfactory  bulb.     (Gordinier  after  Van 

Gehuchten) 212 

87.  Horizontal  section  of  the  cerebrum  through  genu  and  below 

splenium  of  corpus  callosum,  fornix  and  choroid  tela 
turned  back  to  show  inter-brain  and  third  ventricle. 
{Original) 217 

88.  Dissection  of  brain  to  show  geniculate  bodies,  optic  tract, 

nucleus  amygdalae,  etc.     (Aiter  Morrises  Anatomy)   .    .   219 

89.  Transverse  section  of  the  brain  in  the  line  of  the  pyramidal 

tracts,  showing  basal  ganglia,  internal  capsules,  corpus 
callosum,  lateral  and  third  ventricles,  etc.  Viewed  from 
front.     (Morrises  Anatomy  Siiter  Toldt) 224 

90.  The  optic  path.     (Original) 227 

91.  Section  of  mid-brain  through  superior  coUiculi  and  the 

apparent  origin  of  the  oculomotor  nerve.     (Original)   .    230 

92.  Section  of  the  mid-brain  cutting  the  inferior  coUiculi  of  the 

corpora  quadrigemina.     (Original) 231 

93.  Horizontal  and  sagittal  section  through  internal  capsule, 

much  enlarged.     (Original) 242 

94.  Diagram  of  internal  capsule  in  colors.     (Original)      .    .    .    243 

95.  A  diagram  showing  motor  and  muscle-sense  paths,  motor 

red,  sensory  blue.  (After  Gordinier' s  Central  Nervous 
System) 245 

96.  Transverse  section  of  cerebrum,  cutting  corpus  callosum, 

anterior  commissure  and  optic  chiasma.  Viewed  from 
front.  Commissural  fibers.  (Morris's  Anatomy  after 
Toldt) 252 

97.  Long  association  fibers  as  related  to  the  convex  surface  of 

the  cerebral  hemisphere.     (Compiled) 254 

98.  Long  association  fibers  as  related  to  the  medial  surface  of 

the  cerebral  hemisphere.     (Compiled) 256 

99.  Long  association  fibers  revealed  by  an  oblique  antero- 

posterior dissection.     (Compiled  after  Curran  and  G.  E. 

Smith) 257 

100.  Long  association  fibers  located  diagrammatically  in  a  fron- 


LIST    OF   ILLUSTRATIONS  XXXUl 

Fig.  Page 

tal  section  of  the  cerebral  hemisphere.    (After  Cunning- 
ham)   258 

loi.  Dorsal  view  of  inter-brain,  mid-brain  and  cerebellum.     Su- 
perior surface  of  cerebellum.     (Original) 264 

102.  Anterior  aspect  of  cerebellum.     (Original) 266 

103.  Dissection  of  rhombencephalon  to  show  brachium  conjunc- 

tivum,  brachium  pontis  and  corpus  restiforme.     (Gor- 
dinier,  Sappey  after  Hirschfeld  and  Leveille) 267 

104.  Median    section    of    cerebellum,     pons    and    medulla. 

(Original) 268 

105.  Median  section  of  cerebellar  vermis,  showing  the  arbor 

vitse,  and  the  lobules  of  the  vermis.     (Original)   ...    270 

106.  Inferior  surface  of  cerebellum.     (Original) 274 

107.  Sagittal  section  of  cerebellum,  cutting  nucleus  dentatus. 

(Original) 277 

108.  Section  of  cerebellar  gyrus  made  parallel  with  its  free 

border.     Diagrammatic.     (Cunningham  after  Kolliker) .   280 

109.  Section  across  a  cerebellar  gyrus  at  a  right  angle  to  the 

free    border.     Diagrammatic      (Gordinier    after     Van 

Gehuchten) 281 

no.  Horizontal  section  of  cerebellum  cutting  nuclei  and  brachia 

conjunctiva.     (Morrises  Anatomy  after  Toldt) 284 

III.  Anterior  aspect  of  mid-brain,  pons  and  medulla.     (After 

Morrises  Anatomy) 291 

1X2.  Dorsal  surface  of  pons  and  medulla.     (Morris's  Anatomy 

modified  from  Spalteholz) 294 

113.  Superior  transverse  section  of  the  pons.     (Original)  .    .    .   301 

114.  Inferior  transverse  section  of  the  pons  together  with  the 

cerebellum.     (Original) 304 

115.  Stained  superior  section  of  pons;  medulla  ted  fibers  are 

stained  black,  gray  substance  is  light.     (Original) .    .    .   306 

116.  Inferior  transverse  section  of  the  pons,  not  including  the 

cerebellum.    Stained  so  that  meduUated  fibers  are  black. 
(Original) 308 

117.  Diagrammatic   superior  section  of   the  pons   in   colors. 

Red  tracts  are  descending;    blue  tracts  are  ascending. 
(Original) 310 

118.  Diagrammatic  inferior  section  of  pons  in  colors.     The  red 

are  descending  tracts;  the   blue  are  ascending  tracts. 
(Original) 312 


XXxiv  LIST   OF   ILLUSTRATIONS 

Fig.  Pag= 

119.  Diagram   of   the   auditory   paths   in    the   pons.     (After 

Morrises  Anatomy) 3^4 

120.  Transverse  section  of  medulla  from    an   embryo  of  91 

mm.     {McMurrich  after  His.) 317 

121.  Transverse  section  of  the  medulla  from  an  embryo  of  8 

weeks.     (McMurrich  after  His.) 318 

122.  Roof  and  lateral  walls  of  fourth  ventricle,  and  its  chorioid 

plexuses.     (After  Morris's  Anatomy) 322 

123.  Section  of  medulla  oblongata  near  the  pons.     {Original)   .   328 

124.  Section  of  the  medulla  oblongata  at  the  middle  of  olive. 

(Original) " 331 

125.  Section  of  the  medulla  oblongata  at  the  fillet  decussation. 

(Original) 334 

126.  Section  of  the  medulla  oblongata  at  the  pyramidal  decus- 

sation.    (Original) 337 

127.  Mid-olivary  section  of  medulla;  white  substance  stained 

black,  gray  substance  is  light.     (Original) 340 

128.  Diagrammatic  mid-olivary  section  of  medulla;  descending 

tracts  are  red,  ascending  tracts  are  blue.     (Original)   .   343 

129.  Section  of  medulla  at  the  fillet  decussation;  white  sub- 

stance stained  black,  gray  substance  is  light.  (Original)  346 

130.  Diagrammatic  section  at  the  fillet  decussation;  red  tracts 

are  descending,  blue  tracts  are  ascending.     (Original)   .   349 

131.  Section  of  medulla  at  the  pyramidal  decussation;  white 

matter  is  stained  black,  gray  matter  is  light.  (Original) .   352 

132.  Diagrammatic  section  at  the  pyramidal  decussation;  red 

tracts    are     descending,     blue     tracts    are    ascending. 
(Original) 3^^ 

133.  Nuclei  of  the  cerebral  nerves  in  the  medulla,  pons,  mid- 

brain, inter-brain,  and  olfactory  bulb.     Motor  (or  gen- 
,  etic)  nuclei  red,  terminal  (or  sensory)  nuclei  blue.     (After 
Morris's  Anatomy) 357 

134.  Three  forms  of  neurones  found  in  genetic  nuclei  by  Edward 

F.  Malone  (Amer.  Jour.  Anat.,  Vol.  15)   . 373 

135.  Meninges   of    the    spinal   cord:    A.  Transverse    section. 

(After  Key  and  Retzius.)     B.  Anterior  view.     (After 
Ellis.)     (Morris's  Anatomy) 374 

136.  Diagrammatic  section  of  the  spinal  meninges  and  spinal 

cord.     (After  Morris's  Anatomy) 375 


LIST   OF   ILLUSTRATIONS  XXXV 

Fig.  Page 

137.  The  arteries  and  veins  in  the  spinal  cord.     Diagrammatic. 

(After  Morris's  Anatomy) 377 

138.  Posterior  view  of  the  spinal  cord,  the  dura  mater  and  the 

arachnoid  being  laid  open  and  turned  aside.     {Brubaker 
after  Sappey) 380 

139.  Sections  of   the  spinal  cord:    A.  The  cervical.     B.  The 

thoracic.     C.  The  lumbar,   and  D.    The  lower  sacral. 
(Original) 381 

140.  Stained  sections  of  spinal  cord,  sixth  cervical  and  eighth 

thoracic  segments.     (After  Morris's  Anatomy)    ....   383 

141.  Stained    sections    of    spinal    cord;    third  lumbar,  fourth 

sacral  and  the  coccygeal  segments 384 

142.  Tracts  of   fibers    and    columns   of   cells,  in  the  cervical 

region    of    the    cord.     Diagrammatic.     (In  part  after 
Bruce  Sind  Cunningham) 385 

143.  Tracts   of   fibers  in  thoracic    region  of    cord.     Diagram- 

matic   386 

144.  Tracts   of   fibers   and   columns   of   cells   in    the  lumbar 

region    of    the    cord.     Diagrammatic.     (In  part  after 
Bruce  and  Cunningham) 391 

145.  Tracts    of     fibers    and   cell    columns    in    sacral   region 

of   cord.     Diagrammatic.     (In   part  after  Bruce  and 
Cunningham) 392 

146.  Transverse   sections   of   embryos:    A.  Four   and   a  half 

weeks.     B.   About   three   months.     (McMurrich  after 
Sis.) 397 

147.  Mode  of  origin  of  anterior  and  posterior  roots  of  spinal 

nerves.     (After  His) 398 

148.  The  roots  of  the  spinal  nerves.     Diagrammatic.  (Original)  399 

149.  Direct  motor  paths  from  cerebral  cortex  to  cerebral  and 

spinal  nerve.     Diagrammatic.     (Original) 428 

150.  Indirect    efferent    paths     to     the    spinal    nerves.     Dia- 

grammatic.    (Original) 431 

151.  Common  afferent  paths,  muscular,  sympathetic  and  tac- 

tile, by  way  of  the  posterior  column  and  dorsal  spino- 
cerebellar tract.     Diagrammatic.     (Original) 434 

152.  Common  sensory  paths,  pain,  temperature  and  touch,  by 

way    of    ventral    spino-cerebellar    and    spino-thalamic 
tracts.     Diagrammatic.     (Original) 438 


XXXVl  LIST   OF   ILLUSTRATIONS 

Fig.  Page 

153.  Chief  elements  of  the  olfactory  bulb.     (Gordinier  after 

Van  Gehuchten)      442 

154.  The  chief  retinal  elements.     (Aitei  Brubaker's  Physiology) .   443 

155.  The  optic  path.     (Original) 444 

156.  A  simple  spinal  reflex  arc.     (Brubaker  after  Moral  and 

Dayon) 449 

157.  A  more  complicated  spinal  reflex  arc,  involving  the  fas- 

ciculi proprii.     (Brubaker  after  Kolliker) 450 

158.  A  reflex  arc  with  both  a  somatic  and  visceral  efferent 

limb;  pre-ganglionic  and  post-ganglionic  sympathetic 
fibers.     (After  Morris's  Anatomy.) 451 


BRAIN  AND  SPINAL  CORD 


CHAPTER   I 
THE  MENINGES  OF  THE  BRAIN 

(Meninges  Encephali) 

The  meninges  of  the  brain  and  spinal  cord  are  three  in 
number.  They  are  derived  from  the  mesenchyme  which  grows 
around  the  neural  tube  in  the  early  embryo  and  difiFerentiates 
into  three  membranes,  representing  dura  mater,  arachnoid  and 
pia  mater.  A  potential  subdural  space  separates  the  external 
membrane,  the  dura  mater,  from  the  subjacent  arachnoid;  . 
while  a  considerable  subarachnoid  space,  filled  with  fluid,  inter- 
venes between  the  arachnoid  and  the  underlying  pia  mater. 
The  pia  mater  adheres  intimately  to  the  surface  of  the  brain  and 
cord.  Besides  enveloping  the  brain  and  cord,  each  membrane 
forms  protecting  sheaths  for  the  cerebral  and  spinal  nerves 
piercing  it. 

In  fishes  there  is  a  single  vessel-bearing  meninx,  the  primitive 
pia  mater,  investing  the  brain  and  cord.  That  primitive  pia 
mater  of  fishes,  in  the  salamander  and  other  tailed  amphibians, 
becomes  delaminated  by  a  lymph  space  into  two  layers,  con- 
stituting a  dura  mater  and  a  pia  mater.  Only  in  mammals  does 
a  second  and  somewhat  incomplete  cleavage  of  the  pia  mater 
produce  the  arachnoid  membrane  and  the  subarachnoid  space. 

THE  DURA  MATER  OF  THE  BRAIN 

Dura  Mater  Encephali 

Structure  and  Relations. — It  is  a  very  dense  and  inelastic 
membrane  (pachymeninx)  composed  of  white  fibrous  and  yellow 
elastic  tissue  lined  with  flat  endothelial  cells,  which  constitute  its 


2  THE   MENINGES   OF   THE  BEAIN 

internal  surface.  The  dura  of  the  brain  is  made  up  of  two  layers 
which  are  separable  up  to  the  eighth  or  tenth  year,  viz.,  an  outer 
endosteal  layer  and  an  inner  meningeal  layer.  The  external 
layer  constitutes  the  endosteum  of  the  cranial  bones.  It  is 
their  nutrient  membrane.  In  children  it  is  closely  adherent  to 
the  cranial  bones  of  which  it  forms  the  real  periosteum;  but  it  is 
attached  chiefly  at  the  foramina  and  along  the  sutures  in  adults. 
Through  the  cranial  foramina  and  sutures  it  is  continuous  with 
the  external  periosteum.  The  meningeal  layer  of  the  dura  is  the 
more  extensive  as  it  is  folded  into  the  great  fissures  of  the  brain, 
forming  the  processes  of  the  dura  and  greatly  increasing  its 
protective  function.  It  fuses  pretty  closely  with  the  external 
layer  after  the  tenth  year.  In  the  adult  the  internal  layer  of  the 
dura  separates  from  the  outer  layer  only  over  the  apex  of  the 
petrous  bone,  to  form  Meckel's  space  for  the  semilunar  ganglion 
(Gasseri);  at  the  foramina,  to  form  sheaths  for  the  nerves;  and, 
along  the  sinuses,  to  form  their  internal  boundary  and  to  pro- 
duce the  great  incomplete  partitions,  called  processes. 

Processes  {Processus  durce  matris) . — From  the  inner  layer  of 
the  dura  the  great  processes  are  formed.  The  falx  cerebri 
and  falx  cerebelli  hang  vertically  in  the  longitudinal  fissure  of 
the  cerebrum  and  the  posterior  notch  of  the  cerebellum;  and, 
into  the  transverse  fissure  of  the  cerebrum,  extends  horizontally 
the  tentoriiun  cerebelli.  The  falx  cerebri  (Figs,  i,  and  4)  is 
attached  in  front  to  the  crista  galli  and  behind  to  the  crucial 
eminence  and  superior  surface  of  the  tentorium;  the  falx  cere- 
belli (Fig.  i),  which  is  absent  in  our  domesticated  animals  and 
small  in  man,  continues  from  the  inferior  surface  of  the  ten- 
torium, along  the  occipital  crest,  to  the  posterior  border  of  the 
foramen  magnum.  The  bony  attachment  of  the  tentorium 
cerebelli  (Fig.  2)  is  to  the  center  of  the  crucial  eminence  and  its 
horizontal  arms  forward  to  the  petrous  bone;  and,  then,  it  is 
along  the  superior  border  of  the  petrous  bone  to  the  clinoid 
processes  of  the  sphenoid.  Between  its  clinoid  attachments 
there  is  a  deep  bay,  the  incisura  tentorii,  which  transmits  the 
mid-brain. 

The  horizontal  arms  of  the  crucial  eminence  feebly  represent 


SINUSES  3 

the  osseous  part  of  the  tentorium  which  forms  a  prominent  shelf 
in  the  horse.  The  diaphragma  sellae  is  a  small  centrally 
perforated  sheet  of  meningeal  dura  which  covers  the  hypophy- 
seal fossa. 

Sinuses  (Sinus  durce  matris). — ^Large  venous  passages  lined 
with  endothehal  cells,  and  called  sinuses,  are  situated  between 


Fig.  I. — Sagittal  section  of  skull,  showing  falx  cerebri,  falx  cerebelli,  part  of 
tentorium  cerebelli  and  sinuses.  (After  Morrises  Anatomy.) 
a.  Falx  cerebri,  b.  Superior  sagittal  sinus,  c.  Inferior  sagittal  sinus,  d.  Great  cerebra^ 
vein.  e.  Straight  sinus,  f.  Tentorium  cerebelli.  g.  Transverse  sinus,  h.  Superior 
petrosal  sinus,  i.  Palx  cerebelli.  j.  Seventh  and  eighth  nerves,  k.  Ninth,  tenth,  and 
eleventh  nerves.  1.  Twelfth  nerve,  m.  Second  cervical  nerve,  n.  Fourth  nerve,  o.  Third 
nerve,  p.  Second  nerve,  q.  Middle  meningeal  artery,  r.  Internal  carotid  artery,  s. 
Vertebral  artery,  t.  Fifth  nerve,  u.  Sixth  nerve,  v.  Inferior  petrosal  sinus,  w.  First 
cervical  nerve,     x.  Ligamentum  denticulatum. 


the  layers  of  the  dura  (Figs,  i,  2,  3  and  4).  In  the  convex  and 
in  the  free  borders  of  the  falx  cerebri  are,  respectively,  the 
superior  sagittal  sinus  {s.  sagittalis  superior)  and  the  inferior 
sagittal  sinus  {s.  sagittalis  inferior).  The  superior  (Fig.  i) 
extends  from  the  foramen  caecum  back  to  the  confluens  sinuum 


4  THE   MENINGES    OF    THE   BRAIN 

(torcular  Herophili),  located  at  the  internal  occipital  protuber- 
ance. Having  run  through  the  posterior  two-thirds  of  the 
concave  border  of  the  falx  cerebri,  the  inferior  sagittal  sinus 
joins  the  great  cerebral  vein  at  the  margin  of  the  tentorium  and 


Fig.  2, — Horizontal  section  of  skull,  showing  tentorium  cerebelli,  tentorial  notch 
and  sinuses.     (After  Morris's  Anatomy.) 

a.  Infundibulum.  b.  Internal  carotid  artery,  c.  Optic  tract,  d.  Third  nerve,  e. 
Basis  pedunculi.  f.  Cerebral  aqueduct  (Sylvii).  g.  Quadrigeminal  body.  h.  Falx  cerebri. 
i.  Tentorium  cerebelli.  j.  Straight  sinus,  k.  Crista  galli.  1.  Optic  nerve,  m;  Spheno- 
parietal sinus,  n.  Middle  cerebral  artery,  o.  Anterior  cerebral  artery,  p.  Posterior 
communicating  artery,  q.  Cavernous  sinus,  r.  Superior  cerebellar  artery,  s.  Posterior 
cerebral  artery,  t.  Superior  petrosal  sinus,  u.  Freeborder  of  tentorium  bounding  tentorial 
notch.     V.  Transverse    sinus,     w.  Superior    sagittal    sinus. 


forms  the  straight  sinus  (s.  rectus).  The  latter  runs  through 
the  middle  of  the  tentorium  to  the  confluens  (Fig.  2).  The 
occipital  sinus  {s.  occipitalis)  traverses  the  falx  cerebelli  from  the 
foramen  magnum  upward  to  the  same  point.     In  the  confluens 


SINUSES  5 

sinuum  the  transverse  sinuses  {s.  transversi)  rise  (Fig.  2). 
Grooving  the  horizontal  arms  of  the  crucial  ridge,  each  runs 
outward  in  the  tentorium  to  the  base  of  the  petrous  bone,  where 


Fig.  3. — Sinuses  in  the  base  of  the  cranium,  also  meningeal  arteries. 
(After  Morrises  Anatomy.) 
a.  Meningeal  branch  of  anterior  ethmoidal  artery,  b.  Meningeal  branch  of  posterior  eth- 
moidal artery,  c.  Middle  meningeal  artery,  d.  Ophthalmic  division  of  fifth  nerve,  e. 
Third  nerve,  f.  Cavernous  sinus,  g.  Fourth  nerve,  h.  Auditory  and  facial  nerves,  i. 
Superior  petrosal  sinus,  j.  Inferior  petrosal  sinus,  k.  Petro-squamosal  sinus.  1.  Acces- 
sory nerve,  m.  Sigmoid  part  of  transverse  sinus,  n.  Posterior  meningeal  branch  of  verte- 
bral' artery,  o.  Left  marginal  sinus,  p.  Left  transverse  sinus,  q.  Superior  sagittal  sinus. 
r.  Circular  sinus,  s.  Carotid  artery,  t.  Sixth  nerve,  u.  Basilar  artery,  v.  Basilar 
plexus  of  veins,  w.  Auditory  artery,  x.  Vertebral  artery,  y.  Glossopharyngeal  and 
vagus  nerves,  z.  Anterior  spinal  artery,  aa.  Hypoglossal  nerve,  bb.  Accessory  nerve. 
cc.  Right  marginal  sinus,     dd.  Occipital  sinus,     ee.  Right  transverse  sinus. 


it  receives  the  superior  petrosal  sinus;  it  then  turns  downward 
through  the  sigmoid  fossa,  communicates  with  the  occipital 
sinus  and  unites  with  the  inferior  petrosal  sinus  in  the  jugular 
foramen.     Situated  on  either  side  of   the   sella    turcica    is  a 


6  THE   MENINGES    OF   THE   BRAIN 

continuation  of  the  ophthalmic  vein,  the  large  cavernous  sinus 
(s.  cavernosus)  (Fig.  3),  which  receives  at  the  superior  orbital 
fissure  the  spheno-parietal  sinus  {s.  alcB  parva),  the  course  of 
which  is  along  the  posterior  border  of  the  lesser  wing  of  the 
sphenoid  bone.  At  the  posterior  cHnoid  process  the  cavernous 
sinus  divides  into  the  superior  petrosal  sinus  {s.  petrosus  superior) 
and  the  inferior  petrosal  sinus  {s.  petrosus  inferior) .  The  sinus 
inter  cavernosus  anterior  and  sinus  intercavernosus  posterior 
extend  across  the  hypophyseal  fossa,  and  join  the  two  cavernous 
sinuses  together,  and  these  four  communicating  sinuses  consti- 
tute the  circular  sinus  {s.  circularis)  (Fig.  3) .  From  the  bifurca- 
tion of  the  cavernous  sinus  at  the  apex  of  the  petrous  bone,  the 
petrosal  sinuses  run  outward  along  the  corresponding  superior 
and  inferior  borders  of  that  bone.  The  superior  petrosal  sinus 
(Figs.  I  and  3)  empties  into  the  transverse  sinus  at  the  base  of 
the  petrous  bone;  the  inferior  petrosal  sinus ^  in  its  course  to  the 
jugular  foramen,  is  joined  to  its  fellow,  across  the  basilar  process 
of  the  occipital  bone,  by  the  basilar  plexus  {p.  hasilaris)  and,  in 
the  jugular  foramen,  unites  with  the  transverse  sinus  in  forming 
the  internal  jugular  vein. 

Arachnoid  Granulations  (Fig.  30). — Along  and  within  the 
superior  sagittal,  the  straight,  the  transverse,  the  petrosal  and 
the  cavernous  sinuses  are  the  granulationes  arachnoideales  (Pac- 
chionian bodies).  These  granulations  are  enlarged  villi  of  the 
arachnoid  (Fig.  4)  and  seem  to  afford  an  outlet  for  the  sub- 
arachnoid fluid  into  the  sinuses.  They  are  said  to  make  their 
appearance  between  the  third  and  seventh  years  and  to  be 
more  numerous  and  larger  in  the  male  sex.  Some  of  them  by 
absorption  produce  depressions  in  the  cranial  bones  called 
foveolcB  granulares. 

The  arteries  which  supply  the  dura  are:  (i)  The  anterior 
meningeal  from  the  anterior  ethmoidal  branch  of  the  ophthal- 
mic. (2)  The  middle  meningeals,  viz.,  the  great  and  the  small 
middle  meningeal  from  the  internal  maxillary,  the  meningeal 
branch  of  the  lacrimal  and  of  the  internal  carotid,  and  the 
meningeal  branch  of  the  ascending  pharyngeal  which  enters  the 
middle  fossa  of  the  cranium  through  the  lacerate  foramen.     (3) 


MENINGEAL  ARTERIES  7 

The  posterior  meningeal  arteries,  which  rise  from  the  ascending 
pharyngeal,  the  occipital  and  the  vertebral  and  are  distributed 
to  the  dura  over  the  posterior  cranial  fossa. 

The  great  middle  meningeal  artery  {arteria  meningea  media) 
is  much  the  largest  and  is  most  important  (Fig.  5) .  It  overlies 
the  motor  and  somaesthetic  areas  of  the  brain  and  is  the  most 
frequent  seat  of  meningeal  hemorrhage.  Like  the  other  menin- 
geal arteries  it  is  usually  accompanied  by  two  veins.  Ascend- 
ing from  the  foramen  spinosum  it  divides  near  the  anterior 


Fig.  4. — Coronal  section  showing  falx  cerebri,  superior  sagittal  sinus  and  arach- 
noid granulations.     (Gordinier  after  Key  and  Retzius.) 
a.  Subarachnoid  space,     b.  Superior  sagittal  sinus,     c.  Arachnoid    granulation    (Pac- 
chioni).     d.  Dura     mater,     e.  Falx     cerebri,     f.  Anterior     cerebral     artery,     g.  Corpus 
callosum. 


border  of  the  squama  into  two  large  branches,  the  anterior  and 
posterior.  The  posterior  runs  horizontally  backward  across  the 
middle  of  the  squama  temporalis,  a  half  inch  above  the  zygo- 
matic arch  and  then  ascends  over  theposterior  half  of  the  parietal 
bone.  The  anterior  branch  runs  upward  a  half-inch  behind  the 
coronal  suture.  It  may  be  located,  according  to  Quain,  at  one 
inch,  at  one  inch  and  a  half,  and  at  two  inches  behind  the 
zygomatic  process  of  the  frontal  bone  and  above  the  zygomatic 
process  of  the  temporal  bone. 

The  sharp  superior  border  of  the  squama  temporalis  fre- 


8 


THE   MENINGES   OF   THE  BRAIN 


quently  cuts  the  branches  of  the  middle  meningeal  at  their 
points  of  crossing,  thus  producing  meningeal  hemorrhage. 

The  following  nerves  give  branches  to  the  dura :  Trochlear 
ophthalmic,  semilunar  gangHon,  vagus  and  hypoglossal  of  the 
cerebral  group;  and  the  sympathetic.  The  motor  fibers  supply 
the  meningeal  arteries. 

Six  Points  of  Difference  in  the  Dura  of  the  Cord.- — Absence  of 

Brporma 


Ophryon 


Basion 


Fig.  5. — Median  section  of  skull  showing  middle  meningeal  artery. 
(After  Morris^  s Anatomy.) 

processes,  of  sinuses,  of  arachnoid  granulations,  and  of  periosteal 
function.  It  is  covered  on  both  surfaces  by  endothelium  and 
is  separated  from  the  vertebrae  by  areolar  tissue,  fat  and  the 
plexus  of  internal  vertebral  veins. 

THE  ARA.CHNOID  OF  THE  BRAIN 

{A  rachnoidea  E  ncaphali) 

The  arachnoid  is  present  only  in  mammals.     It  is  produced 
by  the  delamination  of  the  pia  mater,  as  that  is  seen  in  birds  and 


SUBARACHNOID   SPACES  9 

reptiles.  In  structure  it  is  a  delicate,  fibrous,  web-like  net 
covered  externally  with  endothelium.  Internally  it  is  joined 
to  the  pia  mater  by  innumerable  fibrous  trabeculae,  the  sub- 
arachnoid tissue  (Fig.  4)  because  of  the  incomplete  cleavage  of 
the  pia  mater.  The  trabeculae  are  ensheathed  and  all  sub- 
arachnoid spaces  lined  with  a  single  layer  of  endothelial  cells, 
hence  both  surfaces  of  the  arachnoid  are  formed  of  endothelium. 
Conical  elevations  of  fibrous  tissue  with  their  investing  endo- 
thelium constitute  the  arachnoid  villi  seen  on  the  outer  surface.^ 
Relations. — The  arachnoid  follows  the  inner  surface  of  the 
dura  and  is  prolonged,  as  a  sheath,  upon  the  nerves  which 
pierce  it.  It  does  not  dip  into  the  sulci  of  the  cerebrum  (Fig. 
6) ;  but  only  into  the  transverse,  the  lateral  and  the  longitudinal 
fissures,  and  does  not  reach  to  the  bottom  of  the  latter.  From 
the  pia  it  is  separated  by  the  subarachnoid  spaces  {cava  subar- 
achnoidealia) .  The  anterior  subarachnoid  space  (Fig.  6)  includes 
the  cisterna  pontis,  c.  interpeduncularis,  c.  ambiens,  c.  chiasma- 
tis,  and  the  c.  fossae  lateralis  cerebri.  It  is  located  in  front 
of  the  medulla,  pons  and  mid-brain  and  in  the  lateral  fossa  and 
fissure.  The  posterior  subarachnoid  space  (Fig.  6)  is  located  be- 
hind the  medulla  and  cerebellum.  It  embraces  the  cisterna  cere- 
bellomedullaris,  a  space  between  the  medulla  and  cerebellum, 
and  the  cisterna  venae  cerebri  magnae,  situated  under  the 
splenium  of  the  corpus  callosum  and  along  the  great  cerebral 
vein.  These  two,  the  anterior  and  posterior,  are  the  largest 
subarachnoid  spaces  and  they  contain  much  of  the  subarach- 
noid fluid.  But  in  the  cerebral  sulci  and  fissures  there  are 
streams  of  this  fluid  which  constitute  the  subarachnoid  rivulets. 
The  anterior  subarachnoid  space  has  slit-like  communications 
with  the  inferior  horn  of  the  lateral  ventricle;  the  posterior 
space  communicates  mth  the  fourth  ventricle  (Fig.  8)  through 
the  median  aperture  (apertura  mediana  ventriculi  quarti,  Ma- 
gendii)  and  the  lateral  apertures  {aperturcE  lateral  ventriculi  quarti, 
Key  and  Retzii  or  Lushkce) . 

'Some  authors  consider  this  membrane,  as  just  described  above,  merely  as  a 
visceral  layer  of  the  arachnoid,  and  regard  the  endothelial  lining  of  the  dura 
mater  as  its  parietal  layer.  According  to  such,  therefore,  the  subdural  space  be- 
comes the  arachnoid  space. 


lO 


THE   MENINGES    OF    THE   BRAIN 


The  hypertrophied  villi  of  the  arachnoid,  which  project  into 
the  sinuses,  and  the  perivascular  channels  of  the  capillaries  and 
veins  of  the  brain  form  the  outlets  for  the  subarachnoid  fluid 
into  the  blood  stream. 

The  vessels  seen  for  a  short  distance  in  the  arachnoid  belong 
to  the  pia  mater.  Its  nerves  are  doubtful.  Perhaps  branches 
of  the  mandibular,  of  the  facial  and  of  the  accessory  supply  it. 


Pia  mater    Subarachnoid  space 


Third  ventricle   — " 
Infundibulum 


Arachnoid 


Cisterna  interpeduncularis 
Cisterna  pontis 


Fourth 

ventricle 
Cisterna    cere- 

bello-medul- 

laris 
Median    aper- 
ture (Magendi) 


Fig.  6. — Diagram  of  pia  and  arachnoid,  showing  subarachnoid  spaces. 
(After  Morris's  Anatomy.) 

In  the  arachnoid  of  the  cord  fewer  trabeculae  join  it  to  the  pia; 
and  these,  in  great  part,  are  collected  to  form  a  fenestrated  sep- 
tum in  the  posterior  median  line  (Fig.  97,  A).  The  external 
spinal  veins  are  covered  by  the  spinal  arachnoid,  they  lie 
between  it  and  the  pia. 


THE  PIA  MATER  OF  THE  BRAIN 

{Pia  Mater  Encephali) 

Structure  and  Relations. — It  is  a  vascular  membrane  com- 
posed of  a  close  network  of  veins  and  arteries  held  together  by 
fibro-elastic  areolar  tissue  (Fig.  9) .  The  endothelium  covering 
its  outer  surface  is  continuous  with  that  ensheathing  the  sub- 


CHORIOID   TELAS  II 

arachnoid  trabeculae.  The  pia  closely  follows  the  brain  surface 
(Fig.  6).  Internally,  it  sends  supporting  trabeculae  into  the 
brain,  which  transmit  blood-vessels;  and  externally  it  forms  an 
investing  sheath  for  each  cerebral  nerve. 

The  pia  mater  and  the  arachnoid  constitute  the  leptomeninges. 

Folds. — Two  important  processes  are  formed  by  the  pia 
mater :  ( i )  The  chorioid  tela  of  the  third  ventricle  {tela  chorioidea 
ventriculi  tertii)  is  pushed  forward  into  the  anterior  part  of  the 
transverse  fissure  of  the  cerebrum  between  the  fornix  and  the 
interbrain  (Fig.  6).  Hence  the  old  name,  velum  interpositum. 
It  is  triangular  in  shape,  with  apex  directed  forward  (Fig.  7). 
Each  lateral  border  is  tucked  into  the  chorioidal  fissure  of  the 
cerebral  hemisphere  and  enters  into  the  floor  of  the  lateral 
ventricle,  while  the  median  part  of  the  fold  is  in  the  roof  of  the 
third  ventricle.  Between  the  two  layers  of  this  chorioid  tela  is 
some  areolar  tissue  through  which  run  backward  the  two  in- 
ternal cerebral  veins  and  unite  near  the  base  of  the  tela  to  form 
the  great  cerebral  vein.  The  chorioid  plexuses  of  the  lateral  and 
the  third  ventricles  occupy,  respectively,  the  lateral  borders 
and  the  median  area  of  this  chorioid  tela.  (2)  A  second  fold  of 
pia  mater  is  tucked  into  the  transverse  fissure  of  the  cerebellum, 
dorsal  to  the  medulla  oblongata  and  ventral  to  the  posterior 
median  part  of  the  cerebellum  (Fig.  6) .  It  is  called  the  chorioid 
tela  of  the  fourth  ventricle  {tela  chorioidea  ventriculi  quarti) 
because  its  inferior  layer  enters  into  the  roof  and  contains 
the  chorioid  plexus  of  that  ventricle.  This  lower  layer  invests 
the  posterior  surface  of  the  medulla  and  the  roof-epithelium 
of  the  fourth  ventricle  (Fig.  8).  It  is  pierced  by  three  foramina 
which  are  situated  as  follows:  One  over  each  lateral  angle  of 
the  fourth  ventricle,  the  lateral  apertures  (Key  and  Retzii,  or 
Lushkae),  and  one  over  its  inferior  angle.  The  latter  is  the 
largest  and  is  called  the  median  aperture  (Magendii).  Those 
three  foramina  establish  communication  between  the  posterior 
subarachnoid  space  and  the  fourth  ventricle. 

The  epithelial  cells  of  the  chorioid  plexuses  secrete  the  cere- 
brospinal fluid  and  pour  it  into  the  ventricles,  whence  it  flows 
through  various  apertures  into  the  subarachnoid  spaces.     In- 


12 


THE   MENINGES    OF    THE   BRAIN 


sufficient  flow  through  the  apertures  or  through  the  subarach- 
noid outlets  results  in  internal  or  external  hydrocephalus.  The 
cerebrospinal  fluid  which  fills  the  ventricles,  the  subarachnoid, 


Fig.  7. — Horizontal  section  of  cerebrum.     Fornix  turned  back,  showing  chorioid 
tela  of  third  ventricle,  and  internal  cerebral  veins.     {Original.) 

subdural  and  other  serous  spaces  of  the  central  nervous  system 
is  not  a  mere  exudate  of  serum.  "  It  is  more  like  tears  and  sweat 
than  lymph.     It  lacks  the  corpuscle  content  of  lymph;  it  has 


CEREBRO-SPINAL   FLUID 


13 


only  half  the  alkalinity  of  lymph;  it  has  no  fibrinogen  at  all 
and  only  a  mere  trace  of  any  protein;  and  it  has  from  3-1 1  per 
cent,  more  CO2  than  is  contained  in  lymph.  Cerebrospinal 
fluid  contains  small  amounts  of  sodium  chloride,  of  carbonates, 
phosphates,  urea,  53-61  per  cent,  of  CO2,  a  trace  of  globulin,  of 
glucose,  and,  when  drawn  by  lumbar  puncture,  a  few  lympho- 
cytes." "Its  specific  gravity  is  1006- 1008."  The  normal 
amount  present  at  one  time  is  stated  by  Mott  to  be  100-130 


Frenulum  veli 
Lateral  fillet 

ingula 


Fourth 
ventricle 


v^^  Inferior  medullary 
^  velum 
Chorioid  plexus 

Median  aperture 
(Magendi) 


Fig,  8. — Roof  and  lateral  walls  of  fourth  ventricle,  and  its  chorioid  plexuses. 
(After  Morris's  Anatomy.) 


cc.  It  exists  under  a  normal  tension  of  100-150  mm.  of  sodium 
carbonate  solution,  in  the  horizontal  posture;  and  of  about 
400  mm.  in  the  erect  posture;  this  may  be  increased  to  700 
mm.  or  more  in  pathologic  states  (Kronig)."  (Santee,  H.  E., 
1915:  Important  Anatomic  and  Physiologic  Factors  in  Sub- 
arachnoid Medication,  111.  Med.  Jour.,  March.) 

The  arteries  of  the  pia  mater  supply  the  brain  (Figs.  9,  10, 
1 1  and  1 2) .  They  are  the  anterior,  middle  and  posterior  cere- 
brals; the  anterior  and  posterior  chorioidals;  and  the  anterior 


14  THE   MENINGES   OF   THE  BRAIN 

and  posterior  inferior  cerebellar  and  the  superior  cerebellar 
with  many  branches. 

The  veins  are  more  numerous  than  the  arteries  in  the  pia: 
the  internal  and  great  cerebral  veins,  the  veins  of  the  chorioid 
plexuses  of  the  lateral,  third  and  fourth  ventricles  and  the 
basilar  vein;  the  cerebral  veins;  superior,  medial  and  inferior; 
and  the  superior  and  inferior  cerebellar  veins.  All  of  them 
empty  into  the  sinuses  (see  p.  20). 

Seven  cerebral  nerveS' — 3d,  5th,  6th,  7th,  9th,  loth  and 
nth — and  the  sympathetic  supply  the  pia  mater  and  its  blood- 
vessels. 

The  pia  mater  of  the  spinal  cord  has  two  layers,  the  outer  of 
which  is  the  more  vascular  and  contains  the  spinal  arteries  and 
the  tributaries  of  the  external  spinal  veins.  It  forms  three 
processes,  namely,  the  anterior  septum,  which  occupies  the 
anterior  median  fissure,  and  the  Hgamentum  denticulatum  of 
each  side. 

THE  BLOOD  SUPPLY  OF  THE  BRAIN 

The  brain  is  furnished  with  blood  by  the  internal  carotid  and 
vertebral  arteries  (Fig.  9).  The  internal  carotid  artery  {as 
carotis  interna)  gives  origin  to  the  anterior  and  the  middle  cere- 
bral, the  anterior  chorioidal  and  the  posterior  communicating, 
the  vertebral  artery  {a.  vertebralis)  gives  off  the  anterior  and 
posterior  spinal  and  the  posterior  inferior  cerebellar  and  then 
unites  with  its  fellow  at  the  inferior  border  of  the  pons  and 
froms  the  basilar  artery.  The  basilar  artery  (a.  basilari); 
runs  upward  the  length  of  the  pons  and  terminates  in  the  two 
posterior  cerebral  arteries  and,  furthermore,  gives  off  the  fol- 
lowing collateral  branches,  viz.,  the  anterior  inferior  cerebellar, 
the  pontal,  the  internal  auditory  and  the  superior  cerebellar. 
Certain  of  these  arteries  form  a  wonderful  circular  anastomosis 
at  the  base  of  the  brain,  called  the  arterial  circle  and  the  dis- 
tribution of  that  circle  is  to  the  cerebrum  (Figs.  9  and  10); 
while  the  rhombencephalon  (pons,  cerebellum  and  medulla) 
is  supplied  by  the  remainder  of  the  arteries  above  enumerated. 
It  is  therefore  convenient  to  describe  the  circulation  of  the 


CEREBRAL   ARTERIES 


15 


brain  under  two  heads :      (A)  The  circulation  of  the  cerebrum, 
and  (B)  The  circulation  of  the  rhombencephalon. 

A.  THE  CEREBRAL  CIRCULATION,  ARTERIES 

The  Arterial  Circle  {Circulus  arteriosis,  Willisi).— The 
arteries  which  supply  the  cerebrum  freely  communicate  in  the 
arterial  circle,  which  is  really  a  heptagon  extending  from  a 


Fig.  9. — Arterial  circle  and  its  branches  on  the  base  of  the  brain. 
(After  Morris's  Anatomy.) 
a.  Anterior  cerebral  artery,  b.  Middle  cerebral  artery,  c.  Internal  carotid  artery,  d. 
Postero-median  ganglionic,  e.  Posterior  cerebral  artery,  f .  Superior  cerebellar  artery,  g. 
Anterior  inferior  cerebellar  artery,  h.  Vertebral  artery,  i.  Posterior  inferior  cerebellar 
artery,  j.  Anterior  communicating  artery,  k.  Antero-lateral  ganglionic.  1.  Anterior 
chorioid.  m.  Posterior  communicating  artery,  n.  Posterior  chorioid.  o.  Basilar  artery. 
p.  Hemisphere  of  cerebellum  cut  away.     q.  Anterior  spinal  artery. 

point  in  the  longitudinal  fissure  anterior  to  the  optic  chiasma, 
back  to  the  pons  (Fig.  9).  It  is  about  an  inch  and  a  half  long, 
and  from  a  half  to  one  inch  in  transverse  diameter.  In  front 
are  the  anterior  cerebral  arteries  converging  forward  from  the 


1 6  THE    MENINGES    OF    THE   BRAIN 

internal  carotids  and,  through  the  anterior  communicating 
artery  (a.  communicans  anterior),  uniting  just  as  they  enter  the 
longitudinal  fissure  of  the  cerebrum.  These  vessels  form  three 
sides  of  the  heptagon  and  the  front  of  the  circle.  On  either 
side,  the  posterior  communicating  artery  {a.  communicans 
posterior)  which  connects  the  internal  carotid  with  the  pos- 
terior cerebral  artery,  forms  the  lateral  boundary  of  the  circle. 
The  posterior  cerebral  arteries  bound  the  circle  behind,  and  so 
complete  it  (Fig.  lo).  The  large  distal  branches  of  the  arteries 
which  are  connected  with  the  arterial  circle  are  distributed 
chiefly  to  the  cortex  and  medulla  of  the  hemispheres;  while  the 
small  proximal  branches  supply  the  gangha  of  the  cerebrum. 
The  former  belong  to  the  cortical  system  (Ai),  the  latter  to  the 
ganglionic  system  (A 2). 

Ai.  The  Cortical  System  of  Arteries. — The  cortical  arterial 
system  comprises  the  distal  portions  of  the  anterior,  middle  and 
posterior  cerebral  and  the  chorioidal  arteries.  The  branches  of 
these  great  vessels  pierce  the  hemispheres  perpendicularly  to  the 
surface.  They  are  distributed,  the  short,  to  the  cortex,  and  the 
long,  to  the  medulla  of  the  hemispheres.  To  a  limited  extent 
they  anastomose  with  one  another,  but  they  do  not  communi- 
cate with  the  ganglionic  system. 

The  anterior  cerebral  artery  {a.  cerebri  anterior.  Figs.  9  and 
12),  a  branch  of  the  internal  carotid,  runs  forward  and  toward 
the  median  line  above  the  optic  nerve  and  enters  the  longi- 
tudinal fissures;  it  is  here  joined  to  its  mate  by  a  very  short 
artery,  the  anterior  communicating.  Winding  around  the  genu 
of  the  corpus  callo^um,  it  runs  back  on  the  medial  surface  of  the 
hemisphere  to  the  occipito-parietal  sulcus.  It  gives  origin  to  the 
antero-median  ganglionic  arteries,  and  to  four  groups  of  cortical 
branches:  (i)  The  medial  orbital  artery  {Figs,  g  a,nd  10)  which 
supplies  the  medial  orbital  gyrus,  the  gyrus  rectus,  the  optic 
chiasma  and  the  olfactory  bulb,  tract,  medial  and  intermediate 
striae,  triangle,  and  parolfactory  area.  (2)  The  anterior  medial 
branch  (Fig.  12)  which  enters  the  anterior  parts  of  the  gyrus 
cinguli  and  superior  frontal  gyrus  on  the  medial  surface  and  of 
the  superior  and  middle  frontal  gyri  on  the  convex  surface. 


CEREBRAL   ARTERIES  1 7 

(3)  The  intermediate  medial  branches,  which  are  distributed  to 
the  middle  part  of  the  gyrus  cinguU,  to  the  paracentral  lobule 
and  to  the  upper  portions  of  the  superior  frontal  and  the  anterior 
and  posterior  central  gyri.  (4)  The  posterior  medial  branches, 
which  run  back  to  the  occipito-parietal  sulcus.  They  supply 
nearly  the  whole  corpus  callosum,  the  posterior  half  of  the  gyrus 
cinguli,  a  part  of  the  paracentral  lobule,  the  praecuneus,  and  the 
superior  parietal  lobule. 

The  middle  cerebral  artery  (a.  cerebri  media,  Figs.  10  and  11) 
crosses  the  anterior  perforated  spot  and  runs  in  the  lateral  fissure 
of  the  cerebrum  to  the  posterior  sulcus  circularis  (Reili)  where  it 
breaks  up  into  several  parieto-temporal  branches.  It  gives 
origin  to  the  antero-lateral  ganglionic  arteries,  and  to  four 
cortical  branches:  (i)  The  lateral  orbital  branches  are  dis- 
tributed to  the  anterior,  lateral,  and  posterior  orbital  and  the 
inferior  frontal  gyri.  (2)  The  ascending  frontal,  two  branches, 
which  follow  the  precentral  and  central  sulci,  supply  the 
anterior  central  gyrus  and  the  posterior  fourth  of  the  middle 
frontal  gyrus.  (3)  The  ascending  parietal,  whose  course  is 
along  the  interparietal  sulcus,  furnishes  blood  to  the  posterior 
central  gyrus  and  the  adjacent  parts  of  the  superior  and 
inferior  parietal  lobules.  (4)  The  parieto-temporal  arteries, 
which  comprise  two  polar  branches  to  the  temporal  lobe  and  a 
large  posterior  branch.  The  latter  runs  in  the  posterior 
ramus  of  the  lateral  cerebral  fissure  to  its  upturned  posterior 
end  and  there  bifurcates  into  a  parietal  and  a  temporal  branch, 
which  just  pass  the  anterior  limit  of  the  occipital  lobe.  The 
entire  distribution  of  the  parieto-temporal  arteries  is  to  the 
temporal  pole  and  to  the  superior,  middle  and  part  of  the 
inferior  temporal  gyri;  to  the  major  parts  of  the  supramarginal, 
angular  and  post-parietal  gyri,  and  to  a  very  small  portion  of  the 
superior  and  lateral  occipital  gyri. 

The  posterior  cerebral  artery  {a.  cerebri  posterior),  a  terminal 
branch  of  the  basilar,  lies  in  the  posterior  boundary  of  the 
arterial  circle  and  is  joined  to  the  internal  carotid  by  the  posterior 
communicating  artery  (Figs.  10  and  12).  It  winds  backward 
between  the  mid-brain  and  gyrus  hippocampi  to  the  tentorial 


1 8  THE  MENINGES    OF   THE  BRAJN 

surface  of  the  cerebral  hemisphere  where,  just  beyond  the 
splenium  of  the  corpus  callosum,  it  terminates  in  the  calcarine 
and  occipito-parietal  branches.  From  the  posterior  cerebral 
arteries  originate  the  postero-median  and  the  postero-lateral 
gangHonic,  and  two  or  more  posterior  chorioidal  arteries  and 
three  cortical  branches:  (i)  The  temporal  branches,  often  an 
anterior,  middle  and  posterior  temporal,  which  supply  the 
hippocampal  and  the  fusiform  gyri  and  a  part  of  the  lingual  and 
of  the  inferior  temporal  gyrus. 

(2)  The  calcarine  artery,  which  runs  along  the  fissure  of  the 
same  name  and  suppHes  the  cuneate  and  Kngual  gyri;  also  the 
pole  and  the  lateral  and  superior  gyri  of  the  occipital  lobe.  (3) 
The  occipito-parietal  artery,  a  single  branch,  which  runs  along 
the  sulcus  occipito-parietaHs  over  the  supero-medial  border  to 
the  convex  surface  of  the  cerebral  hemisphere  and  is  distributed 
to  the  cuneus,  the  praecuneus  and  the  superior  occipital  gyrus. 

The  posterior  chorioidal  arteries  {arterice  chorioidece  poste- 
rior es,  Figs.  7,  9  and  10)  two  or  more  in  number  are  branches  of 
the  posterior  cerebral  which  run  forward  in  the  transverse  and 
chorioidal  fissures  of  the  cerebrum  to  the  chorioid  plexuses  of 
the  lateral  and  third  ventricles  (Fig.  7). 

The  anterior  chorioidal  artery  (a.  chorioidea  anterior)  rises 
from  the  internal  carotid  artery  just  proximal  to  its  anterior 
and  middle  cerebral  branches,  and  runs  backward  and  outward 
along  the  optic  tract  to  the  anterior  inferior  end  of  the  chorioidal 
fissure,  which  it  enters  (Fig.  10).  It  terminates  in  the  chorioid 
plexus  of  the  inferior  horn  of  the  lateral  ventricle,  and  gives 
collateral  branches  to  the  optic  tract,  the  gyrus  hippocampi, 
the  fascia  dentata,  the  hippocampus,  the  crus  of  the  fornix  and 
the  posterior  part  of  the  internal  capsule. 

A2.  The  Ganglionic  System  of  Arteries. — Small  arteries 
from  the  arterial  circle  and  from  the  cerebral  arteries  near  the 
circle  constitute  this  system  (Fig.  10).  The  arteries  pass  to 
their  distribution  without  communicating  with  one  another  or 
with  the  cortical  arteries.  They  are  the  end-arteries  of  Cohn- 
heim.  Between  the  cortical  and  ganglionic  systems,  there  is  an 
area  poorly  supplied  with  blood.     That  is  the  area  of  cerebral 


ARTERIAL   CIRCLE 


19 


Fig.  10, — Arterial  circle  and  its  branches  on  the  base  of  the  cerebrum. 
(Gordinier  after  Buret.) 

On  the  left  side  of  the  brain  the  temporal  lobe  is  cut  away  so  as  to  open  the  inferior  and 
posterior  horns  of  the  lateral  ventricle.  The  mid-brain  is  divided  close  above  the  pons  and 
the  posterior  cerebral  arteries  are  cut  at  their  origin  from  the  basilar. 

Ganglionic  arteries:  am.  Antero- median  group  arising  from  the  anterior  cerebral,  al. 
Antero-lateral  group,  from  the  middle  cerebral,  pm,  pi  (on  the  optic  thalamus).  Postero- 
median and  postero-lateral  groups,  from  the  posterior  cerebral. 

Chorioidal  arteries:  a  ch.  Anterior,  from  the  internal  carotid,  p  ch  (on  the  splenium). 
Posterior,    from   the   posterior   cerebral. 

Cortical  arteries:  i,  i.  Medial  orbital,  from  the  anterior  cerebral.  2.  Lateral  orbital. 
3.  Ascending  frontal.  4.  Ascending  parietal,  and  5.  temporo-parietal  from  the  middle 
cerebral.  6.  Anterior  temporal,  7.  posterior  temporal,  and  8.  occipital,  from  the  posterior 
cerebral. 


20  THE   MENINGES    OF    THE   BRAIN 

softening  in  old  age.  The  ganglionic  system  of  arteries  is  made 
up  of  six  groups  of  small  vessels:  The  antero-median,  the 
right  and  left  antero-lateral,  the  postero-median  and  the  right 
and  left  postero-lateral. 

The  antero-median  ganglionic  arteries  rise  from  the  anterior 
cerebrals  in  front  of  the  optic  chiasma  (Fig.  lo).  They  supply 
the  chiasma,  the  lamina  terminalis,  the  rostrum  of  the  corpus 
callosum,  the  septum  pellucidum  and  the  head  of  the  caudate 
nucleus. 

The  antero-lateral  ganglionic  arteries  take  their  origin,  on 
either  side,  from  the  middle  cerebral  artery,  a  little  outside  the 
arterial  circle  (Fig.  lo).  They  pierce  the  anterior  perforated 
substance  and  are  distributed  to  the  striated  body,  internal 
capsule  and  thalamus.  The  largest  one  of  this  group  is  the 
lenticulo -striate  artery.  It  supplies  the  greater  part  of  the  corpus 
striatum.  On  account  of  its  frequent  rupture,  it  is  called  the 
artery  of  cerebral  hemorrhage  (Charcot) . 

Postero-median  Ganglionic  Arteries.— These  are  branches 
of  the  posterior  cerebral  and  posterior  communicating  arteries 
(Figs.  9  and  lo).  They  supply  the  interpeduncular  structures, 
the  peduncles  and,  after  piercing  the  posterior  perforated  sub- 
stance, the  walls  of  the  third  ventricle  and  the  medial  parts  of 
the  thalami. 

Postero-lateral  Ganglionic  Arteries.— ^They  rise,  on  either 
side,  from  the  posterior  cerebral  artery  after  it  has  wound  around 
the  base  of  the  peduncle  (Fig.  lo).  They  are  distributed  to  the 
posterior  part  of  the  thalamus;  the  geniculate,  quadrigeminal 
and  pineal  bodies ;  the  quadrigeminal  brachia  and  the  pedunculus 
cerebri.  The  superior  cerebellar  arteries  send  several  branches 
to  the  dorsum  of  the  mid-brain,  and  complete  the  arterial  supply 
of  the  cerebrum. 

VEINS  OF  THE  CEREBRUM 

The  Internal  Veins  of  the  Cerebrum.^The  veins  of  the  cere- 
brum {vencB  cerebri)  are  classed  as  internal  and  external.  The 
trunks  of  the  internal  veins  are  located  largely  in  the  chorioid 
tela  of  the  third  ventricle,  near  the  apex  of  which  the  internal 


INTERNAL  VEINS  OF  CEREBRUM 


21 


cerebral  vein  is  formed:  while  at  the  base  of  this  chorioid  tela 
the  internal  cerebral  vein  unites  with  its  mate  in  forming  the 
great  cerebral  vein. 

The  internal  cerebral  vein  (v.  cerebri  interna)  is  formed  by 
the  union  of  the  chorioidal,  the  terminal  and  the  vein  of  the 
septum  pellucidum.  It  runs  backward  between  the  layers  of  the 
chorioid  tela  of  the  third  ventricle  (Fig.  7),  receiving  several 
small  collaterals  from  the  tela,  from  the  pineal  and  quadrigem- 
inal  bodies  and  the  corpus  callosum;  and,  finally,  it  receives  the 
basilar  vein  from  the  inferior  surface  of  the  cerebral  hemisphere. 


Fig,  II. — Middle  cerebral  artery  and  branches.     (Gordinier  after  Quain  and 

Charcot.) 

CENT.    Antero-lateral  group  of   ganglionic  arteries,     i.  Lateral  orbital  artery.    2.  Ascend- 
ing frontal  artery.    3.  Ascending  parietal  artery.    4.  Parieto-temporal  artery. 

Under  the  splenium  of  the  corpus  callosum  it  joins  the  internal 
cerebral  vein  of  the  opposite  side  and  forms  the  great  cerebral 
vein. 

The  great  cerebral  vein  (v.  cerebri  magna,  Galeni)  is  a  short, 
thick,  median  trunk,  a  half -inch  long  (Fig.  i).  At  the  posterior 
border  of  the  tentorial  notch  it  is  joined  by  the  inferior  sagittal 
sinus  and  then  continued  as  the  sinus  rectus.  This  short  vein 
receives  collateral  tributaries  from  the  gyrus  cinguli,  from  the 
medial  and  tentorial  surfaces  of  the  occipital  lobe  and  from  the 
superior  surface  of  the  cerebellum  (Cunningham). 


22  THE   MENINGES   OF    THE  BRAIN 

Small  nameless  internal  veins  issue  from  all  parts  of  the  ex- 
terior surface  of  the  cerebrum  and  form  the  external  veins. 

The  External  Veins  of  the  Cerebrum. — The  external  cerebral 
veins  {vence  cerebri  externa)  are  numerous  and  of  large  size. 
They  ramify  in  the  pia  mater  and  in  the  subarachnoid  space. 
They  empty  into  the  dural  sinuses,  as  a  rule,  against  the  current 
in  the  sinuses,  and  they  form  two  principal  groups:  The 
superior  cerebral  and  the  inferior  cerebral,  and  a  very  small 
group,  on  the  medial  cerebral  surface,  called  the  medial  cerebral 
veins. 

The  superior  cerebral  veins  {vence  cerebri  superior es),  twelve 
or  more  in  number,  carry  away  the  blood  from  the  superior 
surface  of  the  hemisphere.  They  run  obliquely  upward  and 
forward  into  the  superior  sagittal  sinus.  Just  before  emptying 
into  the  sinus  they  receive  most  of  the  medial  veins. 

The  Medial  Cerebral  Veins  {VencB  cerebri  mediales). — They 
drain  the  marginal  part  of  the  medial  surface  of  the  hemisphere. 
The  veins  of  this  group  which  do  not  empty  into  the  superior 
cerebral  veins  unite  and  form  the  inferior  sagittal  sinus,  and  the 
anterior  cerebral  vein  which  drains  much  of  the  medial  surface. 

The  inferior  cerebral  veins  {vence  cerebri  inferiores)  drain  the 
base  of  the  cerebrum  and  the  lower  border  of  its  convex  sur- 
face. On  the  tentorial  surface  of  the  hemisphere,  from  three  to 
five  of  these  veins  empty  into  the  transverse  and  superior 
petrosal  sinuses.  Those  from  the  temporal  and  frontal  lobes 
empty  into  the  spheno-parietal  sinus  and  cavernous  sinus, 
excepting  the  small  anterior  cerebral  vein  and  the  deep  middle 
cerebral  vein,  which  unite  with  the  inferior  striate  veins  in 
forming  the  basilar  vein.  The  anterior  cerebral  vein  accompanies 
the  artery  of  the  same  name.  It  drains  the  gyrus  cinguli  and 
corpus  callosum,  chiefly;  and,  in  the  fossa  lateraHs  cerebri, 
unites  with  vessels  that  descend  from  the  corpus  striatum,  the 
inferior  striate  veins,  and  with  the  deep  middle  cerebral  vein. 
The  deep  vena  cerebri  media  drains  the  insula  and  the  opercula, 
in  part,  and  deep  in  the  fissure  runs  medianward  to  the  fossa 
lateralis  cerebri  and  helps  to  form  the  basilar.  The  basilar 
vein  {v.  basilaris),  is  formed  at  the  anterior  perforated  spot  by 


ARTERIES   OF  MEDULLA  23 

the  deep  middle  cerebral,  the  inferior  striate  and  the  anterior 
cerebral  veins.  Running  backward  it  receives  additional  blood 
from  the  interpeduncular  structures,  the  hippocampal  gyrus 
and  the  inferior  horn  of  the  lateral  ventricle,  and  from  the  mid- 
brain, as  it  winds  around  it  to  empty  into  the  corresponding 
internal  cerebral  vein  near  its  termination.  In  the  fissura 
lateralis  cerebri  (Sylvii)  runs  also  a  superficial  vein,  called  the 
superficial  middle  cerebral  {v.  'cerebri  media)  which  receives 
tributaries  from  the  surfaces  adjacent  to  the  posterior  ramus  and 
the  stem  of  that  fissure  and  empties  into  the  cavernous  sinus; 
but  it  may  have  two  other  outlets,  viz.,  the  transverse  sinus  and 
the  superior  sagittal  sinus.  The  connection  occasionally 
established  between  the  superficial  middle  cerebral  vein  and  the 
transverse  sinus  is  called  the  posterior  anastomotic  vein;  while 
the  great  anastomotic  vein  (of  Trolard)  is  produced  when  it  joins 
one  of  the  superior  cerebral  veins.  The  great  anastomotic  vein 
connects  the  superior  sagittal  with  the  cavernous  sinus. 

There  are  no  lymphatic  vessels  in  either  the  brain  or  spinal 
cord;  perivascular  lymph  spaces  carry  the  fluid  to  the  interior 
from  the  subarachnoid  spaces. 

B.  THE  CIRCULATION  OF  THE  RHOMBENCEPHALON 

Bi.  The  medulla  oblongata  is  supplied  with  blood  by  the 
following  branches  of  the  vertebral  artery:  The  posterior  and 
the  anterior  spinal,  the  posterior  inferior  cerebellar  and  several 
short  bulbar  arteries  (Fig.  9).  The  posterior  inferior  cerebellar 
(a.  cerebelli  inferior  posterior)  winds  from  before  backward 
around  the  medulla,  runs  between  the  vagus  and  accessory 
nerves,  enters  the  vallecula  cerebelli  and  gives  branches  to  the 
m.edulla  and  to  the  chorioid  tela  of  the  fourth  ventricle.  The 
anterior  spinal  artery  {a.  spinalis  anterior)  formed  by  the  y-like 
union  of  a  branch  from  each  vertebral  artery,  descends  along  the 
anterior  median  fissure;  and  the  posterior  spinal  artery  (a.  spinalis 
posterior)  of  either  side,  rising  from  the  vertebral  near  the  lower 
end  of  the  medulla,  descends  in  front  of  the  posterior  lateral 
sulcus.     Both   distribute  branches   along  their  course.     The 


24 


THE    MENINGES    OF   THE   BRAIN 


^i 


.*;g 


la 

a 


^1| 

•  -H  c  rt 
o  C  o 

o    O    " 

3^  pj 

.<  ^ 

«     .22 


VESSELS   OF   PONS 


25 


branches  for  the  most  part  enter  the  median  raphe  or  follow  the 
roots  of  the  bulbar  nerves,  suggesting  the  centrifugal  and 
centripetal  arteries  of  the  spinal  cord  (Fig.  13).  The  veins 
pursue  much  the  same  course  as  the  arteries.  The  anterior 
median  vein  joins  the  ventral  veins  of  the  pons  and  is  drained 
into  the  cerebellar  veins  or  directly  into  the  superior  petrosal 
sinus.  The  posterior  median  vein  bifurcates  y-like  at  the  middle 
of  the  medulla  and  the  two  branches  wind  around  the  medulla 
to  its  anterior  surface  and  empty  into  the  inferior  petrosal  sinus 


•u.  vertedr 


Fig.  13. — Arteries  of  the  medulla  oblongata.     (Modified  from  Gordinier  after 

Diiret.) 

a.  spin.  post.     Posterior  spinal  artery,     a.yertebr.     Vertebral  artery,     a.  spin.  ant.     Anterior 

spinal  artery. 

or  the  basilar  plexus.  Issuing  from  the  medulla  with  the  roots 
of  the  ninth  to  the  twelfth  cerebral  nerves  are  three  or  four  small 
veins,  the  radicular  veins,  which  run  into  the  occipital  and 
inferior  petrosal  sinuses  (Cunningham).  Both  arteries  and 
veins  possess  perivascular  lymph  spaces,  but  there  are  in  the 
medulla  no  lymphatic  vessels. 

B2.  The  pons  VaroHi  is  supplied  by  the  pontal,  the  superior 
cerebellar  and  the  posterior  cerebral  branches  of  the  basilar 
artery  (Fig.  9).  The  short  and  transverse  branches  of  the 
basilar  artery,  the  pontal  arteries  {aa.  pontales).  furnish  the 


26 


THE   MENINGES    OF    THE   BRAIN 


greater  portion  of  blood  to  the  basilar  part  of  the  pons,  while 
the  superior  cerebellar  artery  supplies  the  superior  medullary 
velum  and  the  brachia  conjunctiva  cerebelli.  The  branches 
enter  the  median  raphe,  also  the  substance  of  the  pons  elsewhere, 
especially  along  the  nerve  roots,  and  run  at  right  angles  to  the 
surface  into  it.  The  deep  veins  of  the  pons  run  forward  and  form 
a  plexus  on  its  surface  which,  according  to  Cunningham,  is 
drained  by  a  superior  eferent  into  the  basilar  vein  and  by  an 
inferior  efferent  into  the  cerebellar  veins  or  the  superior  petrosal 


Fig.  14. — Median  section  of  embryonic  brain  of  the  third  month. 

{McMurrich  after  His.) 

I.  Myelencephalon.     11.  Metencephalon:  i.  Pons,  2.  Cerebellum.     HI.  Isthmus'rhomb- 

encephali.     IV.   Mesencephalon:  i.  Pedunculi,  2.  Corpora  quadrigemina.     V.   Diencephalon 

I.  Pars  mammillaris  hypothalami,  2.  Thalamus,  3.  Epithalamus.     VI.  Telencephalon:  i. 

Pars'optica  hypothalami,  2.  Corpus  striatum,  3.  Rhinencephalon,  4.  Neopallium. 

sinus.  There  are  no  lymphatic  vessels  in  the  pons;  but,  as  else- 
where in  the  central  nervous  system,  there  are  lymph  spaces 
about  the  blood-vessels. 

B3.  The  blood  supply  of  the  cerebellum  is  furnished  by 
three  pairs  of  arteries  (Fig.  9).  The  superior  cerebellar,  from 
the  basilar,  supplies  all  the  superior  surface  except  a  narrow 
zone  at  the  posterior  border;  the  anterior  inferior  cerebellar, 
also  from  the  basilar,  and  the  posterior  inferior  cerebellar,  from 
the  vertebral,  supply  the  inferior  surface  and  the  posterior 
part  of  the  superior  surface. 


CEREBELLAR   ARTERIES  27 

The  Superior  Cerebellar  Artery  {A.  cerebelli  superior). — 
Rising  from  the  basilar  just  behind  the  posterior  cerebral,  from 
which  it  is  separated  by  the  oculomotor  nerve,  it  winds  dorsally 
around  the  mid-brain  to  the  sulcus  lateralis,  where  it  bifurcates 
into  a  medial  and  a  lateral  branch  (Fig.  9) .  The  medial  branch 
continues  along  the  trochlear  nerve  in  the  groove  between  the 
cerebellum  and  the  mid-brain  almost  to  the  median  line;  and 
then,  bending  backward,  runs  along  the  superior  worm  of  the 
cerebellum  to  its  posterior  extremity.  It  distributes  branches 
to  the  geniculate  bodies,  corpora  quadrigemina,  tela  chorioidea 
ventriculi  tertii  and  posterior  surface  of  the  pons,  besides  the 
vermis  superior  cerebelli  and  the  medial  part  of  the  superior 
surface  of  the  hemisphere.  The  lateral  branch  of  the  superior 
cerebellar  artery  passes  from  its  point  of  origin  near  the  sulcus 
lateralis  of  the  mid-brain  onto  the  superior  surface  of  the  cere- 
bellum. It  runs  backward  a  half-inch  from  the  border  of  that 
surface,  giving  off  collaterals  along  its  course.  The  lateral 
branch,  together  with  the  medial,  supplies  the  superior  cerebellar 
surface  almost  as  far  back  as  the  horizontal  sulcus  of  the  cere- 
bellum, along  which  the  superior  cerebellar  artery  anastomoses 
with  both  the  inferior  cerebellar  arteries. 

The  anterior  inferior  cerebellar  artery  (a.  cerebelli  anterior 
inferior,  Fig.  9)  is  given  off  by  the  basilar  near  the  junction  of 
its  inferior  and  middle  thirds.  (Sometimes  it  is  replaced  by 
two  or  three  small  vessels.)  It  runs  lateralward,  behind  the 
flocculus,  keeping  close  to  the  anterior  border  of  the  hemisphere. 
In  its  course  it  passes  anterior  to  the  abducent  nerve  and 
posterior  to  the  facial  and  auditory  nerves.  It  supplies  the 
anterior  part  of  the  under  surface  and  border  of  the  cerebellar 
hemisphere. 

The  posterior  inferior  cerebellar  artery  {a.  cerebelli  inferior 
posterior,  Fig.  9)  is  the  largest  branch  of  the  vertebral  and  is 
given  off  just  before  the  vertebral  arteries  unite  and  form  the 
basilar.  Passing  first  between  the  root-bundles  of  the  hypo- 
glossal nerve  and  then  between  those  of  the  accessory  and  vagus 
nerves,  the  posterior  inferior  cerebellar  artery  bends  at  a  right 


28  THE   MENINGES    OF   THE   BEAIN 

angle  backward  and  runs  between  the  medulla  and  the  cere- 
bellar hemisphere,  where  it  divides  into  a  medial  and  a  lateral 
branch.  The  medial  branch  follows  the  sulcus  valleculae  and 
gives  branches  to  the  medial  part  of  the  hemisphere  and  the 
vermis  inferior.  It  anastomoses  with  its  fellow  of  the  opposite 
side.  The  lateral  branch,  runs  lateralward  from  the  posterior 
cerebellar  notch  over  the  inferior  surface  of  the  hemisphere; 
its  terminal  branches  wind  around  the  postero-lateral  border  and 
communicate  with  the  superior  cerebellar  artery  on  the  upper 
surface  of  the  hemisphere.  The  undivided  trunk  of  the  pos- 
terior inferior  cerebellar  artery  gives  small  branches  to  the 
medulla  oblongata  and  supplies  the  chorioid  tela  of  the  fourth 
ventricle. 

The  internal  cerebellar  veins  bring  the  blood  from  the  interior 
of  the  organ  and  pour  it  into  the  superior  and  inferior  external 
veins. 

The  superior  external  cerebellar  veins  {vence  cerebelli  supe- 
riores)  converge  forward  into  a  medial  vein,  which  empties  into 
the  great  cerebral  vein,  and  several  lateral  veins,  which  end  in 
the  transverse  or  the  superior  petrosal  sinus. 

The  inferior  external  cerebellar  veins  {vence  cerebelli  infe- 
rores)  also  form  one  small  medial  vein,  which  runs  backward 
and  upward  either  into  the  straight  or  transverse  sinus,  and  a 
number  of  lateral  veins.  The  lateral  inferior  cerebellar  veins 
terminate  in  the  inferior  petrosal  and  in  the  occipital  sinus. 

Ljmiphatics. — There  are  no  lymphatic  vessels  in  the  cere- 
bellum. Perivascular  lymph  spaces  carry  out  the  lymph  from 
the  whole  brain  and  spinal  cord  and  pour  it  chiefly  into  the 
subarachnoid  space. 

TABLE  I. 

EMBRYOLOGIC  DIVISIONS  OF  THE  BRAIN 

In  accordance  with  its  development  the  brain  or  encephalon 
is  naturally  divided  into  three  embryologic  divisions  which 
comprise  the  derivatives  of  the  anterior,  the  middle  and  the 
posterior  brain  vesicles  (Fig.  14).  In  the  adult  form  it  has  two 
great  divisions,  cerebrum  and  rhombencephalon. 


SUBDIVISIONS    OF  BRAIN 


29 


Cerebrum 


I.  Fore-brain,  or 
Prosencephalon 
(Ant.  vesicle) 


I.  End-brain,    or 
Telencephalon 


II.   Mid-brain,  or  ' 
Mesencephalon 
(Middle  vesicle) 


2.  Inter-brain,    or 
Diencephalon 


Pedunculi 
Cerebri 


Cerebral  Hemispheres 

Corpus  Callosum 

Fornix 

Anterior  Commissure 

Septum  Pellucidum 

Lamina  Terminalis 

Tuber  Cinereum 

Optic     Chiasma    (grows 

into  it) 
Lateral  Ventricles 
Foramina      interventric- 

ularia 
Aula  of  third  Ventricle. 

Ihalami 

Corpora  Mammillaria 
Corpus  Pineale 
Corpora  Geniculata 
Third      Ventricle,      ex- 
cepting the  aula. 


Bases  Pedunculi 
Substantia  Nigra 
Tegmenta 

Cerebral    Aqueduct 
Sylvius) 


(of 


Lamina 
Quadrigemina 


Rhombencephalon 
(Post,  vesicle) 


I.  Metencephalon 
(Hind-brain) 


/  Corpora  Quadrigemina. 
\  Brachia. 

(  Isthmus  Rhombencephali 
J  Cerebellum,  Pons 
1  Upper    half    of    Fourth 
Ventricle 


2.  Myelencephalon 
(Marrow-brain) 


I  Medulla  Oblongata 

\  Lower    half    of    Fourth 

[      Ventricle 

The  cerebrum  embraces  the  fore-brain  and  the  mid-brain,  as 

shown  by  the  table.      So  we  may  make  a  more  comprehensive 

division  of  the  brain  into  only  two  grand  divisions :     The  great 

brain  or  cerebrum  and  the  rhombencephalon  (Fig.  15).     We  may 

now  simplify  the  above  table  as  follows: 

I.     Cerebrum,  embracing — 

End-brain,  or  Cerebral  Hemispheres,  etc. 

Inter-brain. 

Mid-brain. 


30 


THE   MENINGES   OF   THE  BRAIN 


II.  Rhombencephalon,  comprising— 
Isthmus. 
Cerebellum. 
Pons. 
Medulla  Oblongata. 


Olivary  body- 


Cerebrum 


•Cere- 
bellum   [  Metencephalon 

■n        /'T7«.^7.v^     I  1  Rhomben- 

(^Medulla  oblongata) 


2  « 
c 


■ "  Pars  cervicalis 


Pars  thoracalis 


'r  '  Pars  lumbalis 


Pars  sacralis  or 
conus  meduUaris 


Spinal  cord 
{medulla  spinalis) 


Fig.  is. — Divisions  of  the  brain.     Diagrammatic.     (After  Morris's  Anatomy.) 


CHAPTER  II 

GENERAL  CONSIDERATIONS  OF  THE  BRAIN  OR 
ENCEPHALON 

Before  taking  up  the  special  study  of  the  cerebrum  the 
student  should  notice  certain  prominent  features  of  the  entire 
brain.  To  do  this  the  arachnoid  and  pia  mater  must  be  re- 
moved, and  great  care  and  patience  should  be  exercised  to 
preserve  the  integrity  of  the  brain  substance  and  to  guard 
against  evulsion  of  the  roots  of  the  cerebral  nerves. 

The  human  brain  forms  the  greatly  expanded  superior  ex- 
tremity of  the  cerebrospinal  axis.  It  is  derived  from  three 
sac-like  dilatations  of  the  epiblastic  neural  tube,  called  the 
anterior,  the  middle  and  the  posterior  brain-vesicles  (Fig.  i6). 

Origin. — The  nervous  system  is  derived  from  the  epihlast 
because  that  layer  is  most  exposed  to  environmental  stimuli; 
and,  therefore,  becomes  specialized,  by  the  operation  of  this 
obligatory  function,  for  the  reception  of  those  stimuli  and  for 
the  correlation  and  transmission  of  impulses  adapted  to  the 
preservation  of  the  organism.  The  anlage  of  the  nervous  sys- 
tem is  a  dorso-median  thickening  of  the  epiblast,  called  the 
neural  plate  (or  medullary  plate) .  This  anlage  almost  surrounds 
the  embryonic  mouth,  represented  by  the  blastopore.  As  the 
most  primitive  function  of  an  organism  is  feeding,  specializa- 
tion is  first  required  about  the  mouth  in  order  that  the  animal 
may  select  the  proper  food  for  its  development.  Hence,  speciali- 
zation begins  about  the  blastopore  very  early,  in  the  two-layer 
stage  of  the  embryo ;  it  differentiates  the  epiblast  into  neural  plate 
and  cuticle  plate.  In  the  neural  plate  the  epiblastic  cells  assume 
the  long  columnar  form  and  rapidly  mold  the  plate  into  two 
elongated  ridges  joined  by  a  transverse  arch  in  front,  like  a  hair- 
pin.    The  neural  groove  lies  between  the  neural  ridges  and  at  the 

31 


32  GENERAL   CONSIDERATIONS    OF   THE   BRAIN 

open,  posterior  end  of  the  hairpin  the  blastopore  is  located. 
These  neural  ridges  continue  to  rise  up  and  arch  toward  the 
median  plane  until  the  neural  groove  is  roofed  over;  the  neural 
tube  is  the  result.  The  approximation  of  the  neural  ridges  is 
first  completed  in  the  cervical  region,  whence  it  extends  in  both 
directions.  For  a  time,  therefore,  the  tube  has  an  opening  at 
each  end,  called  the  neuropore.  The  anterior  neuropore 
closes  quickly;  but  the  posterior  end  of  the  tube  for  a  little 
longer  time  remains  open,  communicating  with  the  exterior 
through  the  posterior  neuropore  and  with  the  archenteron 
through  the  blastopore. 

The  neural  tube  is  well  formed  by  the  fifteenth  day.  The 
head-foremost  movement  of  the  early  vertebrate,  by  the 
multiplication  of  stimuli  to  the  head,  induces  a  more  rapid 
growth  of  the  cephalic  part  of  the  neural  tube.  Hence,  the 
anterio'r  part  is  much  larger  than  the  posterior  part  of  the 
tube;  it  constitutes  the  encephalic  portion  and  presents  the 
three  primary  brain  vesicles,  the  anterior,  middle  and  posterior, 
out  of  which  the  brain  is  evolved.  The  slender  part  of  the 
neural  tube,  caudal  to  the  brain  vesicles,  forms  the  spinal 
cord. 

In  the  formation  of  the  neural  tube,  the  margin  of  the  neural 
plate  is  lifted  up  into  a  slight  crest  on  either  side  of  the  tube;  it 
is  called  the  neural  crest.  The  neural  crest  breaks  up  into  the 
anlagen  of  the  sensory  nerve  ganglia.  It  probably  furnishes 
the  bipolar  cells  of  the  sympathetic  ganglia,  also;  but  not  the 
multipolars  of  those  ganglia  (Froriep  and  Kuntz) .  The  latter 
point  needs  further  investigation.  After  four  weeks  of  em- 
bryonic life  the  neural  tube  presents  five  brain-vesicles,  formed 
by  the  subdivision  of  the  first  and  third  primary  vesicles  into 
two;  they  are  called  the  secondary  brain-vesicles  and  are  named, 
from  before  backward,  end-brain,  inter-brain,  mid-brain,  hind- 
brain  and  after-brain  (marrow-brain).  A  sharp  ventral  flex- 
ure at  the  level  of  the  mid-brain,  mesencephalic  flexure,  brings 
the  fore-brain  and  hind-brain  into  close  approximation;  thus,  the 
ventral  aspect  of  the  mid-brain  is  shortened.  Later,  a  dorsal 
flexure,  the  pontine  flexure,  folds  the  rudimentary  cerebellum 


VENTRICLES    OF   BRAIN  33 

backward  over  the  medulla  and  pushes  the  pons  forward  into 
its  very  conspicuous  position  (Fig.  i6,  D  and  E). 

Ventricles.^ — The  cavity  of  the  neural  tube  constitutes 
the  adult  ventricles,  which  form  a  continuous  median  series 
extending  from  the  canal  of  the  spinal  cord  up  to  the  level  of  the 
cerebral  hemispheres;  at  that  level  the  central  cavity  bifurcates 
into  a  branch  for  each  hemisphere  of  the  cerebrum  (Figs.  17  and 
18).  Thus  is  formed  the  lateral  ventricle  in  the  cerebral  hemi- 
sphere and,  below  the  cerebral  hemispheres,  the  median  series  of 
cavities  comprises  the  third  ventricle  in  the  inter-brain,  the 
cerebral  aqueduct  in  the  mid-brain,  and  the  fourth  ventricle  in  the 
rhombencephalon. 

Walls. — The  walls  of  these  simple  embryonic  cavities 
undergo  wonderful  development  and  specialization;  ultimately 
they  produce  all  the  multiform  and  complicated  structures  of 
the  adult  human  brain. 

Superior  View. — The  superior  surface  of  the  brain  is  markedly 
convex  (Figs.  19  and  22).  It  is  elliptical  in  outline,  the  major 
axis  (15-17  cm.)  being  contained  in  the  median  line;  the 
greatest  transverse  axis  (14  cm.)  is  situated  a  little  behind  the 
middle  and  runs  between  the  points  which,  when  the  brain  is  in 
the  skull,  underlie  the  tubera  parietalia.  This  surface  is  closely 
adapted  to  the  interior  of  the  calvaria.  Only  the  great  con- 
voluted hemispheres  of  the  cerebrum  are  visible  from  the 
superior  viewpoint.  The  two  hemispheres  are  separated  by  a 
deep,  median  cleft,  called  the  longitudinal  fissure  of  the  cere- 
brum {fissura  longitudinalis  cerebri)  from  which  the  falx  cerebri 
has  been  removed. 

Posterior  View. — When  the  brain  is  viewed  from  behind,  three 
great  structures  and  two  transverse  fissures  are  visible  (Fig. 
20) :  First,  the  occipital  end  of  the  cerebral  hemispheres  with 
their  irregular  gyri  and  sulci ;  second,  the  transversely  laminated 
cerebelltmi,  lying  below  the  cerebrum  and  separated  from  it  by 
the  transverse  fissure  of  the  cerebnun  {fissura  transversa 
cerebri)',  and  third,  the  inferior  extremity  of  a  relatively  small 
median  structure,  the  medulla  oblongata.  The  cerebellum  is 
especially  characterized  by  its  parallel  crescentic  sulci,  which 


34 


GENERAL  CONSIDERATIONS   OF   THE    BRAIN 


Anterior  primary  reside 


Middle  primary  vesicle 
Anterior  primary  vesi 
Telencephalon 


epiphysis  s 
icle__ 


""  ^'middie  primary  vesicle 
'Posterior  primary  vesicle 

Auditory  vesicle ' 


spinal  cord 


cerebellum 

::.  "Posterior  primal 
vesicle 
.medulla 
oUongala 


olfectory  vesicle-  -• 
optic  vesicle' 

Pontine  fltaure 

cervical  flexure 


D  E 

Fig.  1 6. — Diagrams  of  surface  views  and  sections  of  germinal  areas  showing 
the  development  of  the  primitive  streak,  neural  groove,  neural  tube  and  brain 
vesicles.     (After  Morris's  Anatomy.) 

A.  Earlier  stage,  a.  Germinal  area.  b.  Neural  groove,  c.  Primitive  streak.  B. 
Later  stage,  a.  Germinal  area.  b.  Fore-brain  (rudiment  of  cerebral  hemispheres). 
c.  Optic  vesicle,  d.  First  cerebral  vesicle,  e.  Second  cerebral  vesicle,  f.  Third  cerebral 
vesicle,  g.  Primitive  streak.  A'.  Section  through  area  A  along  the  line  o.  a.  Germinal 
area.  b.  Neural  groove.  B'.  Section  through  area  B  along  line  b.  a.  Germinal  area.  b. 
Neural  crest,  c.  Neural  tube.  C.  Primary  vesicles,  dorsal  view.  D.  Brain  vesicles, 
lateral  view,  showing  mesencephalic  flexure.  E.  Secondary  vesicles  showing  mesencephalic 
and  pontine  flexures. 


BASE   OF  BRAIN 


35 


give  it  a  stratified  appearance.  It  shows  a  partial  subdivision 
into  lateral  hemispheres  produced  by  a  posterior  median  de- 
pression, called  the  posterior  cerebellar  notch,  and  by  a  longitudinal 
groove  on  its  inferior  surface,  called  the  vallecula  cerebelli.  The 
vallecula  is  fitted  over  the  posterior  surface  of  the  medulla. 
The  cerebellum  is,  therefore,  separated  from  the  medulla  ob- 
longata by  a  sharply  curved,  rainbow-shaped  fissure.  That 
fissure  is  the  transverse  fissure  of  the  cerebellum  {fissura 
transversa  cerebelli)  which,  as  already  pointed  out,  is  bridged 
over  by  the  arachnoid  and  contains  the  *  cisterna  cerebello- 
medullaris. 


Fig.  17. — Diagrammatic  horizontal  section  of  vertebrate  brain. 
{Morrises  Anatomy  after  Huxley.) 
a.  Metencephalon.     b.  Thalanus.     c.  Medulla  oblongata,     d.  Cerebellum,     e.  Lateral 
ventricle,     f.  Olfactory    diverticulum,     g.  Lamina    terminalis.     h.  Corpus    striatum,     i. 
Mid-brain,     j.  Pineal    body.     k.  Interventricular    foramen. 


Inferior  View. — The  base  of  the  brain  presents  three  areas, 
situated  in  three  successive  levels,  which  correspond  in  location 
and  extent  to  the  great  fossae  in  the  base  of  the  cranium  (Figs. 
21  and  33).  The  anterior  area,  situated  in  the  anterior  cranial 
fossa,  occupies  the  highest  level;  the  middle  area  is  intermediate 
in  position;  it  occupies  the  middle  fossa  and  together  with  the 
anterior  area  comprises  all  of  the  base  of  the  cerebrum  which  is 
visible  in  the  complete  brain;  and,  the  posterior  area,  which  is 
but  the  base  of  the  rhombencephalon,  is  situated  at  the  lowest 
level  in  the  posterior  fossa  of  the  cranium. 

The  anterior  area  of  the  base  of  the  brain  is  divided  into 
lateral  halves  by  the  longitudinal  fissure  of  the  cerebrum,  and 
separated  from  the  middle  area  by  the  fossa  and  fissura  cerebri 


36 


GENERAL   CONSIDERATIONS    OF    THE  BRAIN 


lateralis.  The  frontal  lobe  of  the  cerebral  hemisphere,  on  either 
side  of  the  longitudinal  fissure,  makes  up  nearly  all  this  area. 
The  inferior  surface  of  the  frontal  lobe  is  concave  and  is  adapted 
to  the  convex  orbital  plate  of  the  frontal  bone;  its  medial  border 
is  most  prominent  and  presents,  near  the  longitudinal  fissure, 
an  elongated  gray  mass,  the  olfactory  bulb  (if  it  has  not  been 
torn  off)  and  a  white  strand,  the  olfactory  tract.  Running  back- 
ward from  the  bulb,  parallel  with  the  longitudinal  fissure  of  the 
cerebrum  to  the  fossa  cerebri  laterahs,  the  olfactory  tract  is  seen 
to  bifurcate  into  two  distinct  striae,  a  medial  and  a  lateral. 
The  middle  area  of  the  inferior  surface  of  the  brain  is  promi- 


k  1  m  n  o 

Fig  1 8. — Diagrammatic  sagittal  section  of  verebrate  brain. 
(Morris's  Anatomy  after  Huxley.) 

a.  Corpora  quadrigemina.  b.  Mid-brain,  c.  Pineal  body.  d.  Cerebellum  (hind- 
brain),  e.  Medulla  oblongata  (after-brain),  f.  Pons  Varolii  (hind-brain),  g.  Lateral 
ventricle,  h.  Cerebral  hemisphere,  i.  Corpus  striatum,  j.  Olfactory  diverticulum,  k. 
Pedunculi  cerebri.  1.  Thalamus,  m.  Inter-brain,  n.  Hypophysis,  o.  Interventricular 
foramen.     4.  Fourth  ventricle,     s.  Aqueduct  of  cerebrum.     3.  Third  ventricle. 


nent  laterally  where  it  is  formed  by  the  temporal  lobes  of 
the  cerebrum.  It  is  depressed  in  its  median  portion  and  thus 
adapted  to  the  hypophyseal  region  of  the  cranial  floor.  This 
median  hypophyseal  region  extends  from  the  end  of  the  longi- 
tudinal fissure,  in  front,  backward  to  a  great  white,  transversely 
striated  eminence,  called  the  pons;  it  contains  several  important 
structures,  viz.,  the  bases  pedunculi;  posterior  perforated  sub- 
stance; the  mammillary  bodies;  tuber  cinereum  and  stem  of  the 
infundibulum;  optic  chiasma,  tracts  and  nerves;  lamina  cinerea 
terminahs;  and  the  anterior  perforated  substance. 

Issuing  from  the  under  surface  of  the  cerebral  hemisphere  and 
running  downward  toward  the  median  line,  there  may  be  seen  a 


BASE    OF  BRAIN  37 

white  Striated  band,  a  half-inch  broad,  called  the  basis  pe- 
diinculi,  which,  on  approximating  its  fellow  in  the  median  plane 
disappears  into  the  pons.  Anteriorly,  the  X-like  optic  chiasma 
(chiasma  opticum)  is  easily  identified  near  the  longitudinal 
fissure;  its  anterior  limbs  are  the  optic  nerves  and  its  posterior, 
the  optic  tracts  (Fig.  21).  The  optic  tract,  when  traced  back- 
ward and  outward,  under  the  overhanging  temporal  lobe,  is 
observed  to  cross  the  basis  peduncuH  at  its  point  of  emergence 
from  the  cerebral  hemisphere.  Thus  the  optic  tract  and  the 
basis  pedunculi  form  the  lateral  boundary  of  a  diamond-shaped 
space  extending  from  the  optic  chiasma,  in  front,  backward  to 
the  pons.  This  is  commonly  called  the  interpeduncular  space. 
You  observe  in  it  three  structures:  (i)  A  gray  eminence  just 
behind  the  optic  chiasma  called  the  tuber  cinereum;  (2)  a  pair 
of  white,  nipple-like  bodies,  an  eighth  of  an  inch  in  diameter, 
known  as  the  white  or  mammillary  bodies  {corpora  mammillaria) , 
and  (3)  a  triangular,  perforated  mass  of  dark  gray  substance, 
called  the  posterior  perforated  substance  {substantia  perforata 
posterior).  In  the  normal  condition,  the  infundibulum  projects 
downward  and  forward  from  the  center  of  the  tuber  cinereum  and 
connects  it  with  the  hypophysis  cerebri;  but  it  is  usually  broken 
in  removing  the  brain  and  the  hypophysis  left  behind  in  the 
hypophyseal  fossa.  ** 

If  the  optic  chiasma  be  drawn  slightly  downward  and  back- 
ward, a  transverse  and  nearly  vertical  sheet  of  gray  matter  will 
be  seen  extending  upward  from  it,  between  the  cerebral  hemi- 
spheres, toward  the  corpus  callosum.  That  is  the  lamina 
cinerea  terminalis.  It  bounds  posteriorly  the  frontal  part  of 
the  longitudinal  fissure  of  the  cerebrum.  Lateral  to  the  optic 
chiasma  and  anterior  to  the  optic  tract,  the  gray  substance  is 
perforated  by  many  vessels;  it  is  called  the  anterior  perforated 
substance  {substantia  perforata  anterior)  to  distinguish  it  from 
a  similar  posterior  region  located  between  the  bases  pedunculi. 

Posterior  Area. — The  posterior  area  of  the  base  of  the  brain 
is  formed  by  the  pons,  the  cerebellum,  and  the  medulla  oblongata, 
which  constitute  the  rhombencephalon  (Fig.  21).  The  pons  and 
medulla  are  median  structures.     They  are  separated  by  a  well- 


38 


GENERAL  CONSIDERATIONS  OF  THE  BRAIN 


marked  transverse  groove,  the  ponto-medullary  groove,  contain- 
ing the  roots  of  the  sixth,  the  seventh,  the  intermediate  and  the 
eighth  cerebral  nerves.  The  transverse  strands  of  the  pons 
traced  lateralward  are  observed  to  form  a  large  round  bundle, 
called  the  brachium  pontis,  which  extends  into  the  hemisphere 


Fig.  19. — Fronto-superior  surface  of  cerebrum.     {Original.) 

of  the  cerebellum  on  either  side.  Between  those  pontine  strands, 
at  the  lateral  border  of  the  pons,  there  should  be  noticed  the 
roots  of  the  great  trigeminal  nerve.  A  sagittal  line  through  this 
nerve  at  its  attachment  to  the  pons  may  be  regarded  as  the 
boundary  between  the  pons  and  the  cerebellar  hemisphere. 


ROOTS  OF  CEREBRAL  NERVES  39 

The  hemispheres  of  the  cerebellum  form  the  lateral  part  of  the 
posterior  area;  their  stratified  appearance  is  already  familiar. 
Inferior  to  the  pons  is  the  medulla  oblongata.  The  medulla  is 
about  an  inch  long  and  three-quarters  of  an  inch  broad  near  the 
pons,  but  measures  less  than  one-half  inch  in  width  at  the  lower 
end.  It  is  partially  divided  into  lateral  halves  by  the  anterior 
median  fissure,  which  is  deep,  above,  but  is  almost  obliterated 
in  the  lower  half  of  the  medulla  by  the  crossing  of  the  lateral 
pyramidal  tracts,  the  decussatio  pyramidum.  On  either  side  of 
the  anterior  median  fissure,  the  student  should  notice,  in  this 
order,  the  pyramid,  the  olive,  and  the  restiform  body.  The 
pyramid  (pyramis)  bounds  the  anterior  median  fissure.  It  is 
an  eighth  of  an  inch  in  width,  is  most  prominent  near  the  pons 
and  tapers  off  inferiorly  because  about  80  per  cent,  of  its  fibers 
cross  over  to  the  opposite  side  and  sink  backward  in  the 
medulla.  It  is  bounded  laterally  by  a  slight  longitudinal 
furrow,  the  anterior  lateral  sulcus  (sulcus  lateralis  anterior) 
which  contains  the  roots  of  the  twelfth  cerebral  nerve,  and 
separates  the  pyramid  from  the  olive  and  from  the  flat  surface 
of  the  lateral  funiculus  of  the  medulla.  The  olive  (pliva) 
occupies  the  upper  half  of  the  lateral  surface  of  the  medulla; 
the  lateral  funiculus,  the  lower  half.  The  olive  is  equal  in 
breadth  to  the  pyramid.  It  is  quite  prominent,  is  white  in 
color  and  is  elliptical  in  outline.  The  posterior  lateral  sulcus 
{sulcus  lateralis  posterior)  separates  it  from  the  restiform  body. 
The  roots  of  the  ninth,  tenth  and  eleventh  cerebral  nerves, 
which  are  contained  in  that  groove  and  the  restiform  body 
which  lies  beyond  it,  can  be  seen  only  by  pressing  aside  the 
hemisphere  of  the  cerebellum. 

The  Roots  of  the  Cerebral  (Cranial)  Nerves  (Fig.  21).— The 
cerebral  nerves  (nervi  cerebrales)  are  numbered  from  before 
backward  according  to  the  order  of  their  points  of  attachment  to 
the  brain  surface.  Those  points  of  attachment  are,  for  the 
motor  roots,  points  of  exit  from  the  brain;  and  are  points  of 
entrance  into  the  brain,  for  all  the  sensory  roots.  The  genetic 
nucleus  {nucleus  originis),  which  is  the  real  origin  of  a  motor 
root,   and   the  terminal  nucleus    {nucleus    terminalis),  which 


40 


GENERAL   CONSIDERATIONS  OF   THE  BRAIN 


contains  the  real  central  termination  of  any  sensory  root,  are 
imbedded  within  the  brain  substance  and  do  not  at  present 
concern  us. 

I.  The  olfactory  nerves  {nervi  olfactorii)  are  the  first.  They 
are  the  nerves  of  smell.  They  are  composed  of  the  peripheral 
olfactory  neurones  whose  cell-bodies  form  the  olfactory  ganglion, 


Fig.  20. — Posterior  view  of  the  brain.     {Original.) 

located  in  the  olfactory  area  of  the  nasal  mucous  membrane. 
The  short  dendrites  protrude  slightly  from  the  mucous  mem- 
brane into  the  nasal  cavity  and  end  in  a  tuft  of  ciha;  the  vari- 
cose axones,  leaving  the  deep  end  of  the  cell-bodies,  plunge 
into  the  tunica  propria  and  ascend  through  the  cribriform  plate 
to  the  olfactory  bulb,  forming  close  plexuses  on  the  way;  they 
are  non-medullated  and  are  collected  into  20  or  30  bundles. 


NERVE    ROOTS  4I 

each  of  which  is  invested  by  a  nucleated  sheath  like  a  neu- 
rolemma. The  fibers  proceed  some  distance  into  the  gray 
substance  of  the  olfactory  bulb,  which  constitutes  the  terminal 
nucleus  of  the  first  nerves,  and  there  branch  richly  and  end  in 
relation  with  the  mitral  and  brush-cells. 

2.  Optic  Nerve  {Nervus  opticus). — The  second  nerve,  the 
nerve  of  sight,  is  really  a  brain  tract  rather  than  a  nerve,  and 
its  fibers  are  imbedded  in  neuroglia  and  do  not  possess  a  neu- 
rolemma. It  rises  in  the  ganglionar  layer  of  the  retina.  Passing 
through  the  chorioid  and  sclera  of  the  eyeball  and  the  optic 
foramen  of  the  sphenoid  bone,  it  enters  ink)  the  optic  chiasma 
where  the  *' nerve"  is  said  to  end;  but  the  fibers  of  the  nerve 
continue  without  interruption  through  the  optic  tracts  and 
their  lateral  roots  to  the'  inter-brain  and  the  mid-brain,  whose 
surfaces  they  pierce;  they  end  in  the  lateral  geniculate  body, 
in  the  pulvinar  of  the  thalamus,  and  in  the  superior  coUiculus 
of  the  quadrigeminal  bodies,  where  the  three  terminal  nuclei 
are  located. 

3.  The  oculomotor  nerve  {n.  oculomotorius)  is  the  great  motor 
nerve  to  the  eye  (Fig.  21).  It  issues  from  the  mid-brain  at  the 
medial  border  of  the  basis  pedunculi,  but  its  origin  is  in  a  mass  of 
gray  substance,  the  genetic  nucleus  {n.  originis),  situated  within 
the  depths  of  the  mid-brain. 

4.  Trochlear  Nerve  {N.  trochlearis) . — The  fourth  is  a  motor 
nerve  to  the  eye  and  is  the  smallest  of  the  cerebral  nerves.  It 
may  be  seen  winding  forward  over  the  basis  pedunculi  (Fig.  21). 
Its  point  of  exit  is  from  the  dorsal  surface  of  the  brain  stem 
at  the  junction  of  the  mid-brain  with  the  hind-brain  (the  isth- 
mus. Fig.  44);  this  emergence  cannot  be  seen  in  the  complete 
brain.  The  genetic  nucleus  of  the  fourth  nerve  is  located  below 
that  of  the  third  in  the  mid-brain. 

5.  Trigeminal  Nerve  (A^.  trigeminus). — The  trigeminal  nerve 
is  a  mixed  nerve,  motor  and  sensory  (Fig.  21).  It  is  attached 
to  the  ventral  surface  of  the  pons  a  little  above  the  middle  of  its 
lateral  border.  The  small  anterior  motor  root,  the  masticator 
nerve  (Bean)  emerges  from  this  point;  but  this  is  the  entrance 
of  the  large  sensory  root,  which  rises  in  the  semilunar  ganglion 


42  GENERAL  CONSIDERATIONS   OF   THE  BRAIN 

(Gasseri)  and  enters  the  pons  close  to  the  emergence  of  the 
motor  root. 

6.  The  abducent  nerve  (n.  abducens)  is  a  motor  nerve  to  the 
eye.  It  issues  from  the  pons  at  its  inferior  border,  or  from 
the  transverse  groove  between  the  pons  and  the  medulla,  just 
above  the  pyramid  of  the  medulla  and  nearly  in  line  with  the 
anterior  lateral  sulcus  (Fig.  21). 

In  the  transverse  groove  between  the  pons  and  the  medulla, 
lateralward  from  the  root  of  the  sixth  nerve,  are  the  roots  of  the 
seventh,  intermediate  and  eighth.  The  seventh  is  smaller  in 
diameter  than  the  eighth  and  medial  to  it  in  position;  the  inter- 
mediate is  between  these  two,  separated  from  the  facial  by  the 
fasciculus  obliquus  pontis  (Figs.  21  and  57). 

7.  The  facial  nerve  {n.  facialis)  is  the  motor  nerve  to  the 
muscles  of  expression  (Figs.  21  and  57).  Rising  from  a  nucleus 
in  the  pons,  it  emerges  from  the  transverse  groove  between  the 
medulla  and  pons.  The  intermediate  nerve  {n.  intermedins)  is 
so  closely  associated  with  the  facial  nerve  that  many  regard  it 
as  the  sensory  root  of  that  nerve;  but  the  intermediate  nerve 
is  in  reality  a  mixed  nerve  with  efferent  fibers  of  vasodilator, 
secretory  and  trophic  functions  and  afferent  fibers  whose 
function  is  taste.  It  may  well  be  called  the  glossopalatine  nerve, 
as  suggested  by  Robert  Bennet  Bean  (Anat.  Rec).  The  eferent 
fibers  rise  from  the  salivary  nucleus  (the  visceral  or  splanchnic 
part  of  the  facial  nucleus)  in  the  pons.  They  issue  from  the 
transverse  ponto-medullary  groove  between  the  facial  and 
auditory  nerves  at  the  point  where  the  afferent  fibers  enter  the 
brain.  The  sensory  part  of  the  intermediate  nerve,  which  is  the 
nerve  of  taste  to  the  anterior  part  of  the  tongue,  takes  its  origin 
in  the  ganglion  geniculi  situated  within  the  canalis  facialis 
(Fallopii);  it  enters  the  brain  through  the  ponto-medullary 
groove. 

8.  The  acustic  nerve  {n.  acusticus)  is  a  sensory  nerve,  having 
two  parts,  the  cochlear  and  the  vestibular  nerves,  and  the 
double  function  of  hearing  and  equilibrium  (Figs.  21,  56  and 
57).  It  rises  from  the  spiral  and  vestibular  ganglia  situated 
in  the  petrous  bone,  and  it  enters  the  brain  at  the  bottom  of 


ACUSTIC   NERVE 


43 


the  transverse  groove  separating  the  pons  from  the  medulla. 
The  roots  of  both  the  seventh  and  eighth  nerves  are  near  the 


Fig.  21. — Base  of  brain.     (Original.) 

a.  Olfactory  bulb.  b.  Olfactory  tract,  c.  Medial  and  lateral  olfactory  striae,  d. 
Trigonum  olfactorium.  e.  Area  parolfactoria  (Brocae).  f.  Anterior  perforated  substance. 
g.  Optic  chiasma.  h.  Optic  tract,  i.  Tuber  cinereum.  j.  In  fundibulum.  k.  Hypo- 
physis. 1.  Corpus  mammillare.  m.  Posterior  perforated  substance,  n.  Basis  pe- 
dunculi.     o.  Sulcus  parolfactorius  anterior.     2  to  12.  the  cerebral  nerves. 

upper  end  of  the  posterior  lateral  sulcus  of  the  medulla  ob- 
longata. The  acustic  nerve  fibers,  like  the  optic,  are  peculiar 
in  that  they  possess  no  neurolemma. 


44  GENERAL   CONSIDERATIONS    OF   THE   BRAIN 

9.  Glossopharyngeal  Nerve  {N.  glossopharyngeus). — This  is 
a  complex  mixed  nerve,  containing  efferent  fibers  (motor,  vaso- 
dilator, secretory  and  trophic)  and  afferent  fibers,  which  are 
both  common  sensory  and  gustatory.  It  is  joined  to  the 
medulla  in  the  bottom  of  the  superior  end  of  the  posterior  lateral 
sulcus,  where  the  efferent  fibers  emerge  and  the  afferent  fibers 
enter  the  brain  (Figs.  21  and  57). 

The  latter  fibers  rise  in  the  superior  and  petrosal  glosso- 
pharyngeal ganglia  situated  in  the  jugular  foramen.  The 
genetic  nucleus  of  the  efferent  fibers  is  located  inside  the 
medulla. 

Behind  the  ninth  nerve  in  the  same  groove  are  the  roots  of 
the  tenth  and  eleventh  nerves.  The  roots  of  the  ninth  and 
tenth  are  situated  between  the  olive  and  the  restiform  body; 
but,  if  the  nerve  trunks  have  been  cut,  it  is  impossible  to  de- 
termine which  of  the  ten  or  a  dozen  root  bundles  belong  to 
each  of  them. 

10.  The  Vagus  Nerve  {N.  vagus) . — The  efferent  fibers  of  the 
vagus,  like  the  glossopharyngeal,  emerge  from  the  posterior 
lateral  sulcus,  and  in  the  same  sulcus  the  afferent  fibers  enter  the 
medulla  (Figs.  21  and  57).  It  is  a  very  complex  nerve.  Its 
efferent  fibers  comprise  motor,  inhibito-motor,  vasodilator, 
secretory,  trophic  and  inhibito-secretory  fibers  (Pawlow) .  The 
afferent  or  sensory  fibers  of  the  vagus  rise  in  the  jugular  and 
nodular  ganglia  of  the  nerve  {g.  jugular e  and  g.  nodosum)  within 
and  just  below  the  jugular  foramen.  Within  the  medulla  are 
the  genetic  nuclei  of  the  efferent  fibers. 

11.  The  accessory  nerve  {n.  accessorius)  is  composed  of  a 
cerebral  and  a  spinal  root  both  of  which  are  efferent  in  function 
(Fig.  57).  The  cerebral  root  (radix  cerebralis)  rises  within  the 
medulla  and  issues  from  the  posterior  lateral  sulcus  below  the 
level  of  the  olive  and  immediately  inferior  to  the  roots  of  the 
vagus.  This  is  distributed  entirely  by  way  of  the  vagus.  The 
spinal  root  (radix  spinalis)  rises  in  the  gray  substance  of 
the  spinal  cord  and,  having  emerged  from  the  lateral  surface 
of  the  spinal  cord  and  passed  through  the  foramen  magnum,  it 
joins  the  cerebral  (accessory)  root  near  the  jugular  foramen. 


MONKEY  S  BRAIN 


45 


Fig.  2  2. — Convex  surface  of  the  left  cerebral  hemisphere  of  the  Macacus  maurus. 

A,c.  sulcus  frontalis  inferior;  b,d.  s.  frontalis  superior,  broken  into  two  parts;  e.  s.  prae- 
centralis  inferior,  continuous  above  with  superior  frontal  sulcus;  f.  s.  praecentralis  superior; 
g,h.  s.  Post-centralis  inferior;  g.  continued  as  s.  horizontalis;  i.  s.  centralis  with  genu  supe- 
rius  and  genu  inferius  opening  backward;  j.  s.  post-centralis  superior;  k.  s.  occipito-parietalis, 
which  receives  the  horizontal  and  on  the  surface  is  continuous  with  the  s.  simialis.  The  latter 
runs  obliquely  downward  and  forward  toward  the  infero-lateral  border  of  the  hemisphere 
(AflFenspalte  or  s.  lunatus) ;  1.  s.  orbito-frontalis;  m.  fissura  cerebri  lateralis  (Sylvii) ;  n.  s.  tem- 
poralis superior;  o.  s.  temporalis  inferior;  p.  s.  occipitalis  lateralis;  q.  s.  occipitalis  inferior. 


Fig. '23. — Insula   (Reilii),   the  frontal,  parietal  and  temporal  opercula  being 

cut  away. 
A. 'anterior  lobule  of  insula  made  up  of  four  very  rudimentary  gyri  breves:  b.  posterior 
lobule  of  insula,  gyrus  longus:  c.  sulcus  centralis  insulae.     {Santee,  Anat.  Rec.'j 


46 


GENERAL   CONSIDERATIONS   OF   THE  BRAIN 


Fig.  24. — Medial  surface  of  right  cerebral  hemisphere  of  the  Macacus  maurus, 

A.  sulcus  rostralis,  or  the  anterior  part  of  the  cingulate  sulcus;  b.  s.  cinguli;  c.  s.  sub- 
parietalis:  d.  s.  occipito-parietalis;  e.  fissura  calcarina  at  its  posterior  end  where  it  bifurcates; 
I.  s.  paroliactorius  posterior:  g.  s.  rhinalis,  very  well  developed;  h.  a  slot  leading  to  the  fissura 
chorioidea,  commonly  calleahippocampal  fissure;  i.  f.  coUateralis;  j.  s.  sagittalis  gyri lingualis. 


Fig.  25. — Base  of  fore-brain  of  the  Macacus  maurus,  the  mid-brain  being  cut 
through  transversely. 

A.  sulcus  olfactorius  and  a  part  of  the  olfactory  tract;  b.  s.  orbitalis,  H-shape;  c.  gyrus  fusi- 
formis;  d.  s.  occipitalis  inferior;  e.  fissura  coUateralis;  f.  s.  sagittalis  gyri  lingualis;  g.  f.  cal- 
carina; h.  s.  occipito-parietalis,  inferior  end.      {Santee,  Anat.  Rec.) 


BRAIN  MEASUREMENTS  AND   WEIGHTS  47 

12.  Hypoglossal  Nerve  (N .  hypoglossus)  .—The  twelfth  is 
the  great  motor  nerve  to  the  tongue  (Figs.  21  and  57).  A  half 
dozen  or  more  radicals  make  it  up;  they  rise  in  the  medulla  and 
issue  in  linear  series  from  the  anterior  lateral  sulcus  of  the 
medulla  between  the  pyramid  and  the  olive.  The  root  bundles 
which  emerge  from  the  same  sulcus  below  the  level  of  the  olive 
belong  to  the  anterior  root  of  the  first  cervical  nerve. 

The  student  should  now  turn  back  to  Table  I.  Study  it 
carefully  and  identify  all  the  primary  and  secondary  divisions 
of  the  brain  (Figs.  14,  15,  16,  17,  18,  and  34). 

BRAIN  MEASUREMENTS  AND  WEIGHTS 

Ethnologic  investigations  of  cranial  capacity  and  brain  weight  reveal  two 
important  general  facts:  first,  the  cultured  and  aggressive  races  possess  the 
larger  brains;  and,  second,  the  cranial  capacity  increases  during  the  rise 
from  barbarism  to  culture  and  power  and,  conversely,  decreases  with  the 
decline  of  a  people.  The  former  fact  is  illustrated  by  the  findings  of  Davis 
(Phil.  Trans.,  1868)  who  estimated  brain  weight  from  cranial  capacity. 
He  gives  the  average  brain  weight  in  the  different  races  as  follows:  Cauca- 
sian, 1335  gm.;  Chinese,  1330  gm.;  Sandwich  Islanders,  1300  gm.;  Malays 
and  North  American  Indians,  1265  gm.;  Hindus,  11 90  gm.;  and  Aus- 
tralian Natives,  1 1 85  gm.  Secondly,  the  brain  of  prehistoric  man,  as  repre- 
sented by  the  "Neanderthal  skull,"  weighed  about  1000  gm.  The 
"Trinil  skull "  contained  a  brain  estimated  at  800  gm.  Again,  E.  Schmidt 
has  discovered  that  the  cranial  capacity  is  smaller  in  the  modern  Egyptians 
than  in  the  mummy  skulls  of  the  Ptolemaic  period  when  Egypt  was  in  her 
prime. 

It  is  also  observed  that  the  brains  of  great  men  are  usually  above  the 
average  size  (E.  A.  Spitzka)  and  that  a  very  diminutive  brain  (below  900 
gm.)  is  never  associated  with  high  mentality  and  is  found  often  in  imbe- 
ciles and  idiots.  Hence,  there  is  some  ground  for  the  popular  behef  that 
the  size  of  the  brain  has  a  direct  relation  to  mental  capacity;  but  such  a 
broad  inference  is  not  warranted  by  other  facts.  Indeed,  a  brain  near  the 
average  size  and  weight,  possessing  some  degree  of  frontal  lobe  predomi- 
nance, is  most  often  associated  with  superior  moral  and  mental  attributes. 
The  area  of  the  frontal  lobe  should  exceed  slightly  the  combined  areas  of 
the  parietal  and  temporal  lobes  in  brains  of  high  types,  according  to  H 
Wagner  (Figs.  22  and  24).  Compare  the  brain  surface  of  the  great 
mathematician,  Prof.  Gauss,  with  that  of  an  ordinary  man,  a  workman. 


48  GENERAL    CONSIDERATIONS    OF    THE   BRAIN 

Surface  Measurements  of  the  Lobes  of  the  Cerebrum 


I     Frontal        Parietal        Temporal     :  Occipital       Island    |  f^^J °iq.^mm. 

"  \  \  \  \  \  ■ 

Gauss 89,545    I     45,493    !     44,062       ]     38,286    |   2,252  219,638 

Workman 72,890        40,142    \     39,880      1     32,490   j   2,270         187,672 

These  measurements  of  H.  Wagner  and  others  indicate  that  the  relative 
size  of  the  frontal  lobe  is  of  prime  importance  to  mental  capacity;  and  such 
a  conclusion  is  further  supported  by  the  facts  that  imbeciles  and  idiots  are 
especially  deficient  in  the  frontal  lobe,  that  the  grade  of  senile  dementia  is 
proportionate  to  the  amount  of  degeneration  in  this  lobe,  and  that  pre- 
dominance of  the  frontal  lobe  is  characteristic  of  the  step  up  from  the 
highest  animal  to  man.  But  surely  the  perfection  of  individual  neurones 
contained  in  the  brain  and  the  completeness  of  their  contact  relations  are 
of  far  more  significance  than  mere  size  and  weight.  Quality  is  of  first  im- 
portance; that  being  present,  then,  quantity  may  signify.  Physiology  has 
shown  that  the  character  of  circulating  fluids,  also,  must  be  taken  into 
account  (Figs.  22,  23  and  24). 

Brain  dimensions  and  weight  vary  with  stature  and  weight  of  body.  As 
a  rule,  the  larger  body  contains  the  larger  brain;  but,  as  the  increased  bulk 
of  body  only  necessitates  increase  of  the  motor  and  sensory  mechanisms 
(and  not  of  the  higher  psychic  mechanisms)  the  relative  size  of  the  brain 
is  lower  in  men  of  large  stature  and  weight  than  in  men  of  average  size. 
Attempts  have  been  made  to  show  that  of  all  animals  man  has  the  largest 
brain  when  it  is  compared  with  the  weight  of  the  body.  They  failed. 
The  Gibbon,  in  this  respect,  has  a  brain  equal  to  man's,  certain  apes  have  a 
greater  brain  relatively,  and  some  very  insignificant  animals  have  a  higher 
ratio  of  brain  to  body  than  man. 

Cranial  configuration  influences  both  brain  measurements  and  weight. 
The  dolichocephahc  brain  with  its  long  polar  and  short  equatorial  axis 
usually  possesses  smaller  area  of  cortex  and  lower  weight  than  the  brachy- 
cephaHc  brain  in  which  the  two  axes  are  more  nearly  equal. 

The  occipito-frontal  axis  of  the  male  brain  measures  from  160-170  mm. 
(6.4-6.8  in.);  of  the  female  brain,  150-160  mm.  (6-6.4  in.).  The  great- 
est transverse  diameter  is  the  same  in  both  sexes,  140  mm.  (5.6  in.).  The 
average  vertical  height  in  both  sexes  is  125  mm.  (5  in.).  The  female  brain, 
though  shorter,  is  equal  in  breadth  and  depth  to  the  male  brain. 

H.  Wagner  has  estimated  the  surface  of  the  cerebral  hemispheres,  by 
covering  them  with  goldleaf,  to  be  equal  to  from  187,000-221,000  sq.  mm. 
(2.1-2.5  sq.  ft.):  this  of  course  represents  the  extent  of  cerebral  cortex. 
The  cortex  varies  in  thickness  from  1.55  mm.  in  the  floor  of  the  small  polar 
sulci  to  5  mm.  in  the  superior  end  of  the  central  gyri.  The  average  is 
3  mm.     In  all  regions,  the  depth  is  greater  in  the  summit  of  a  gyrus  than  in 


BRAIN   WEIGHTS  49 

the  bottom  of  a  sulcus.  It  is  slightly  thicker  in  the  left  hemisphere  and  in 
the  male  brain.  Investing  the  white  substance,  its  weight  comprises  50 
per  cent,  of  the  entire  hemisphere,  though  the  specific  gravity  of  the  cere- 
bral cortex  is  1033  (1029-1038)  and  that  of  the  cerebral  white  substance 
1041  (1036-1043).     The  specific  gravity  of  the  entire  brain  is  1036. 

The  average  weight  of  an  adult  white  man's  brain  is  about  1375  gm. 
(48.5  oz.).  An  adult  white  woman's  brain  averages  1245  gm.  (43.9  oz.). 
After  sixty  years,  the  brain  weight  diminishes  gradually  to  the  extent  of  6  or 
7  per  cent.  E.  A.  Spitzka  has  found  the  average  brain  weight  of  108 
distinguished  men  to  be  1473  gm.;  and  he  found  the  beginning  of  senile 
atrophy  in  these  men  to  be  postponed  10  years  on  an  average.  Villiger 
gives  the  average  weight  of  the  German  brain,  1425  gm.;  the  English  brain, 
1345  gm.;  and  the  French  brain,  1280  gm.  Most  of  these  were  obtained 
from  dissecting  room  specimens. 

E.  A.  Spitzka's  findings  in  108  distinguished  men  (Trans.  Am.  Phil. 
Soc,  1908): 

Average  brain  weight  in  grams 

27  Americans  (U.  S.  and  Canada) 1519 

14  British  and  Scots • 1481 

20  French 1456 

3  8  Germans  and  Austrians 1439 

Grand  average. 1473  .  75 

9  of  various  nationalities  with  nearly  the  same  average. 

According  to  the  estimate  of  Meynert  the  brain  is  made  up  as  follows: 
78.5  per  cent,  fore-brain;  11  per  cent,  mid-brain,  pons  and  medulla,  and 
10.5  per  cent,  cerebellum. 

Cerebrum  equals  seven-eighths  of  the  brain,  rhombencephalon  one- 
eighth.  In  a  male  brain  of  1375  S^-  cerebrum  weighs  1204  gm.  (42.5 
oz.);  cerebellum,  143  gm.  (5  oz.);  and  pons  and  medulla,  28  gm.  (i  oz.). 
The  female  cerebrum  weighs  1074  gm.  (38  oz.);  cerebellum,  143  gm.  (5 
oz.);  and  the  pons  and  medulla,  28  gm.  (i  oz.),  in  a  brain  weighing 
1245  gm. 

The  brain  attains  almost  its  full  weight  in  the  first  six  years;  but  it  con- 
tinues to  increase  slightly  through  youth  and  manhood  up  to  thirty-five  or 
forty  years.  Education  and  experience  increase  it  appreciably  and  they 
contribute  greatly  to  the  complete  development  and  medullation  of  the 
neurones  and  to  the  establishment  of  those  mechanisms  necessary  to  the 
functions  of  the  nervous  system  in  man. 

At  birth  the  male  brain  weighs  about  400  gm.  (14.2  oz.)  the  female  brain, 
380  gm.  (13.4  oz.).  These  weights  are  doubled  in  a  year  and  in  six  years 
they  are  thrice  the  weight  at  birth. 

The  relation  of  brain  to  body-weight  in  the  new  born  is  about  i  to  8,  in 
the  adult  about  i  to  50.  Tiedemann,  gives  the  larger  proportions:  at 
4 


50        GENERAL  CONSIDERATIONS  OF  THE  BRAIN 

birth,  male,  i  to  5.85,  female,  i  to  6.5;  adults  who  died  without  wasting 
disease,  i  to  41. 

Some  over-sized  brains  from  distinguished  men:  Prof.  Gauss,  1492  gm.; 
Prof.  Agassiz,  1512  gm.;  Daniel  Webster,  1516  gm.;  Kant,  the  philoso- 
pher, 1600  gm.;  Thackeray,  1658  gm.;  Cuvier,  1861  gm.;  Ivan  Turgenef, 
2012  gm. 

Cranial  capacities  Cranial  capacities 

(Spitzka)  in  (Spitzka)  in 

cubic  centimeters  cubic  centimeters 

Daniel  Webster 1999 . 5     Dante 1493 

Kant 1740        Bach 1480 

Franz  Joseph  Gall 1692        DesCartes 1706 

Beethoven 1750 

Subnormal  brain-weights  from  celebrated  men:  Dr.  Leibig,  1352  gm.; 
Gambetta,  the  French  statesman,  1294  gm.;  Walt  Whitman,  1282  gm.; 
Dr.  Tiedemann,  1254  gm.;  Dr.  DoUinger,  1207  gm.;  Dr.  Franz  Joseph 
Gall,  the  phrenologist,  11 98  gm. 

J.  Wiglesworth  and  George  A.  Watson  report  an  epileptic  dement  who 
had  a  head  measuring  25  inches  in  circumference  and  a  brain  weighing, 
with  the  pia  and  arachnoid,  2130  gm.  (Brain,  Vol.  36,  Part  I,  p.  31). 

The  elephant  has  a  brain,  in  some  cases,  weighing  4000  gm.,  and  the  large 
whales  one  weighing  3000  gm.  The  gorilla  has  one-third  as  much  brain  as 
man.  A  Borneo  monkey  (Macaccus  maurus)  has  a  brain  weighing  1 1 5  gm. 
The  gorilla  and  monkey  show  marked  deficiency  of  the  frontal  lobes,  when 
compared  with  man  (Figs.  22  and  24).  The  elephant's  and  whale's 
brains  are  surely  made  up  chiefly  of  motor  and  sensory  mechanisms,  the 
psychic  regions  being  very  small. 


CHAPTER  III 
THE  CEREBRUM 

The  cerebrum  with  its  great  hemispheres  is  that  part  of  the 
brain  which  especially  characterizes  man.  In  man  only  do  the 
hemispheres  reach  such  predominant  development.  Though 
they  are  mere  outgrowths  of  the  anterior  brain-vesicle  in  the 
beginning,  they  completely  overshadow  all  other  parts  of  the 
brain  by  the  seventh  month  of  embryonic  life,  extending  farther 
forward,  backward  and  lateralward  than  any  other  part. 
Within  the  cerebrum  lies  the  physical  basis  of  all  conscious 
mental  function;  it  constitutes  the  central  mechanism  of 
thought  and  consciousness.  The  active,  functionating  elements 
of  the  cerebrum  are  the  neurones,  which  constitute  a  little  more 
than  half  its  bulk.  Every  mental  process,  whether  con- 
scious or  unconscious,  is  attended  by  a  mysterious  physico- 
chemical  process  in  certain  neurones.  That  process  consists 
of  an  increased  blood  supply,  increased  metabolism,  altered 
chemical  reaction,  elevation  of  temperature,  and  permanent 
changes  in  the  neurones  that  persist  as  records  or  memories. 
Those  records  are  very  gradually  reduced  in  vividness  by  the 
normal  nutritive  changes,  according  to  Ribot's  law  of  regression; 
but  they  are  never  entirely  eradicated  except  by  degeneration  or 
dissociation  of  the  neurones. 

Reference  to  the  table  given  above  shows  that  the  cerebrum 
is  made  up  of  three  parts:  (i)  The  end-brain,  which  includes 
the  cerebral  hemispheres  and  their  connecting  links;  (2)  the 
inter-brain,  comprising  the  thalami  and  their  associated  nuclei, 
which  with  the  former  constitutes  the  fore-brain;  and  (3)  the 
mid-brain  (Figs.  17,  18,  and  33).  The  cerebrum  is  an  ovoid 
mass,  flattened  inferiorly,  which  fills  the  vault  of  the  cranium 
and  rests,  below,  upon  the  floor  of  the  cranial  cavity  in  the 
anterior  and  middle  fossae  and  upon  the  tentorium  cerebelli  over 

SI 


52 


THE    CEREBRUM 


the  posterior  fossa  (Fig.  2).  It  comprises  seven-eighths  of  the 
entire  brain,  weighing  on  the  average  from  1074-1204  gm. 
(38-43  oz.).  Viewed  from  above,  it  is  sufficiently  round  to 
suggest  a  sphere;  and,  being  divided  in  the  median  line  by  the 
longitudinal  fissure,  the  lateral  halves  are  called  hemispheres. 
The  most  anterior  point  is  the  frontal  pole,  and  the  most 
posterior  is  the  occipital  pole  (Fig.  26).  In  the  floor  of  the 
longitudinal  fissure  of  the  cerebrum  the  corpus  callosum  can  be 
seen  joining  the  hemispheres  together;  and  beneath  it,  con- 
cealed from  view,  are  the  fornix  and  anterior  commissure. 
Those  are  the  connecting  links,  proper,  of  the  hemispheres 
(Figs.  42,  47  and  48).  Inferior  to  them  is  found  the  inter-brain. 
The  latter  forms  an  additional  union  of  the  hemispheres,  as  may 
be  seen  by  viewing  the  base  of  the  brain.  Just  caudal  to  the 
inter-brain  is  the  mid-brain  which  occupies  the  tentorial 
notch  of  the  dura  mater;  and,  situated  in  the  median  line,  is  so 
overhung  by  the  cerebral  hemispheres  as  to  reveal  only  its  an- 
terior surface.  It  resembles  the  inter-brain  in  this  respect. 
Inferiorly  the  mid-brain  joins  the  rhombencephalon.  Their 
plane  of  union  cuts  the  isthmus  (Fig.  56). 

In  studying  the  gross  structures  of  the  cerebrum  it  is  most 
convenient  to  divide  it  into  its  earliest  embryologic  divisions, 
viz.,  the  fore-brain  and  the  mid-brain. 


SECTION  I.    THE  FORE-BRAIN  OR  PROSENCEPHALON 


Fore-brain 


I.  End-brain 


2.  Inter-brain 


Cerebral    Hemispheres    and   their   connecting 

links — 
Corpus  Callosum 
Commissura  Anterior 
Commissura  Hippocampi  (Fornix). 

[  Thalami 

I  Mammillary  Bodies  (of  hypothalamus) 
1  Geniculate  Bodies  (metathalamus) 
I  Pineal  Body  (of  epithalamus). 

In  order  to  fix  important  landmarks  and  to  learn  the  location 
and  relations  of  the  gross  structures  of  the  fore-brain  it  is  neces- 
sary, first,  to  study  in  detail  the  topograhy  of  the  exterior  surface 
and,  then,  the  macroscopic  structures  shown  by  sections.     It  is 


BORDERS    OF   CEREBRAL   HEMISPHERE  53 

that  with  which  the  present  section  deals.  For  the  minute 
anatomy  of  the  cerebral  structures,  see  Section  III  of  the 
Cerebrum. 

SURFACE  OF  FORE-BRAIN 

The  exterior  surface  of  the  fore-brain  is  divided  by  distinct 
borders  into  three  regions,  namely,  the  convex  surface,  the 
medial  surface,  and  the  basal  surface  (Figs.  26,  31  and  33). 
The  basal  surface  comprises  the  orbital  and  tentorial  areas, 
separated  by  the  stem  of  the  fissura  cerebri  lateralis  (Sylvii). 
The  convex  surface  is  separated  from  the  medial  surface  by  the 
supero-medial  border  {mar go  super o-medialis) ,  from  the  tentorial 
area  of  the  basal  surface  by  the  infero-lateral  border  {mar go  infero- 
lateralis,  or  m.  occipitalis  lateralis),  and  from  the  orbital  area  of 
the  basal  surface  by  the  superciliary  border  {mar go  superciliaris) . 
The  medial  orbital  border  {margo  orbitalis  medialis)  separates  the 
orbital  area  of  the  basal  surface  from  the  medial  surface,  and 
the  medial  occipital  border  {margo  occipitalis  medialis)  divides 
the  medial  surface  from  the  tentorial  area  of  the  basal  surface 
(Figs.  19,  26  and  31). 

The  surface  of  the  fore-brain  is  composed  of  a  thin  sheet  of 
gray  matter  varying  in  thickness  from  1.5-5  ^^-  (little  less 
than  one-sixteenth  to  slightly  more  than  one-fifth  of  an  inch). 
That  gray  matter  forms  a  bark-like  covering  for  the  underlying 
white  substance  and  is,  therefore,  called  the  cortex  (Figs.  42  and 
46).  It  is  thrown  into  irregular  elongated  folds  named  con- 
volutions, or  gyri,  by  deep  linear  depressions,  which  greatly 
increase  the  relative  amount  of  cortical  substance.  The  linear 
depressions  are  called  fissures,  or  sulci;  and,  in  consequence  of 
them,  the  gray  substance  is  increased  in  bulk  to  58^^  per  cent, 
of  the  entire  cerebrum  (DeRegibus). 

The  name  fissure  is  properly  appHed,  first  to  those  deep 
furrows  which  represent  clefts  between  embryonic  vesicles,  viz., 
the  median,  vertical  cleft  between  the  cerebral  hemispheres^ 
and  the  two  arched  clefts,  one  between  the  cerebellum  and  the 
cerebral  hemispheres  and  the  other  between  the  cerebellum  and 
the  posterior  surface  of  the  medulla  oblongata  (Figs.  19  and  20)^ 


54  THE    CEREBRUM 

and,  second,  the  deep  linear  depressions  in  the  cerebral  hemi- 
sphere which  indent  the  entire  ventricular  wall  and  produce 
eminences  on  the  interior  surface  are  properly  called  fissures. 
All  other  furrows  in  the  cerebral  surface  are  called  sulci. 

A  satisfactory  explanation  for  the  folding  of  the  cortex  into 
gyri  has  not  been  found.  The  folding  is  rendered  necessary  by 
the  area  of  the  cortex,  since  it  has  three  times  the  extent  of  the 
free,  exposed  surface  of  the  cerebrum;  but  this  does  not  explain 
the  permanence  of  pattern  in  sulci  and  gyri  which  results  from 
such  folding.  The  production  of  cerebral  gyri  must  be  a  posi- 
tive process  based  upon  developmental  factors  not  yet  under- 
stood. Through  a  long  phylogeny  the  functional  demands  of 
different  areas  of  cortex  have  gradually  built  up  these  factors  of 
development  and  they  have  been  rendered  permanent  by  the 
persistence  of  the  same  functional  demands. 

FISSURES  AND  SULCI  OF  CONVEX  SURFACE 

The  convex  surface  of  the  cerebral  hemisphere  {fades  convexa 
cerebri)  is  related  to  two  very  extensive  fissures,  viz.,  the  longi- 
tudinal and  the  transverse.  The  longitudinal  fissure  of  the 
cerebrum  (fissura  longitudinalis  cerebri)  is  the  vertical  median 
cleft  between  the  hemispheres  of  the  cerebrum  (Figs.  19  and 
26).  It  contains  the  falx  cerebri  (Fig.  i).  Its  floor  is  formed 
by  the  corpus  callosum.  The  cerebrum  is  separated  from  the 
cerebellum  by  the  transverse  fissure  of  the  cerebrum  {fissura 
transversa  cerebri,  Figs,  i,  6,  20  and  33).  This  fissure  continues 
forward  above  the  mid-brain,  and  terminates  in  the  cerebrum 
between  the  inter-brain  and  the  fornix,  where  it  is  continuous, 
by  its  lateral  extremities,  with  the  chorioidal  fissures  of  the 
hemispheres.  The  tentorium  occupies  the  posterior  part.  The 
anterior  part  of  the  transverse  fissure  contains  the  chorioid  tela 
of  the  third  ventricle. 

There  are  three  great  furrows  in  the  convex  surface  of  each 
cerebral  hemisphere  which  form  interlobar  boundaries  and  con- 
stitute very  important  landmarks :  The  fissura  cerebri  lateralis, 
the  sulcus  centralis,  and  the  sulcus  occipito-parietalis  (Figs.  26 
and  27). 


LATERAL  FISSURES 


55 


The  lateral  fissure  (fissura  cerebri  lateralis  [Sylvii])  begins 
in  the  fossa  of  the  same  name  at  the  base  of  the  brain  (Fig.  21). 
It  runs  outward  between  the  frontal  and  the  temporal  lobe, 


along  the  lesser  wing  of  the  sphenoid  bone;  and,  turning  up- 
ward, on  the  convex  surface,  it  divides  three-fourths  inch  behind 
the  Sylvian  point  into  an  anterior  horizontal,  and  anterior  as- 
cending and  a  posterior  ramus   (Fig.  27).     Into  the  frontal 


56  THE    CEREBRUM 

lobe  project  the  small  anterior  rami.  They  are  separated  by 
the  foot  (posterior  end)  of  the  inferior  frontal  gyrus,  called  the 
pars  triangularis.  Below  the  anterior  horizontal  ramus  is  a 
knuckle  of  the  same  frontal  gyrus  which  forms  the  pars  orhitalis; 
and,  between  the  ascending  and  posterior  rami,  is  located  the 
pars  opercularis,  constituting  the  connecting  gyrus  between  the 
inferior  frontal  and  central  gyri.  The  inferior  frontal  gyrus 
forms  the  frontal  part  of  the  operculum  (pars  frontalis  operculi). 
The  operculum  (operculum,  a  cover),  covers  the  island.  The 
posterior  limb  of  the  lateral  cerebral  fissure  separates  the  tem- 
poral lobe  from  the  parietal.  Near  the  crotch  and  within  the 
fissure  is  situated  the  island.  A  line  drawn  from  the  Sylvian 
point  to  the  subparietal  point  lies  over  the  posterior  ramus  of 
the  lateral  fissure.  The  Sylvian  point  is  one  inch  and  a  quarter 
(3.2  cm.)  behind  the  zygomatic  process  of  the  frontal  bone  and 
an  inch  and  a  half  (3.75  cm.)  above  the  zygomatic  arch.  The 
subparietal  point  lies  three-quarters  of  an  inch  (1.75  cm.)  below 
the  parietal  tubercle. 

The  Sulcus  Centralis  (Rolandi,  Figs.  26,  27,  28  and  33).— 
Beginning  just  above  the  posterior  limb  of  the  lateral  cerebral 
fissure,  is  the  eentral  sulcus,  which  extends  upward  and  back- 
ward to  the  longitudinal  fissure  of  the  cerebrum.  Its  upper 
extremity  is  about  half  an  inch  (or  5.7  per  cent.)  behind  the 
middle  of  a  line  drawn  from  the  nasal  eminence  to  the  external 
occipital  protuberance.  With  this  sagittal  meridian  the  sulcus 
centralis  forms  an  anterior  angle  of  69  to  74°.  The  average 
Rolandic  angle  is  71°  7'  (Cunningham).  The  sulcus  centralis 
is  three  and  three-eighths  inches  long  and  forms  the  boundary 
between  the  frontal  and  the  parietal  lobe.  It  is  developed  in 
two  parts  a  superior  third  and  an  inferior  two-thirds,  which  join 
at  an  angle  open  backward,  called  the  genu  superius ;  both  parts 
may  present  an  anterior  concavity.  Often  a  concealed  gyrus 
separates  the  two  parts  of  the  sulcus  at  the  genu  superius 
(Fig.  26).  This  superior  genu  is  in  line  with  the  superior  frontal 
sulcus  and  marks  the  probable  location  of  the  trunk  center  and 
the  boundary  between  the  arm  and  leg  areas  in  the  anterior 
central  gyrus.     There  is  a  less  constant  angle,  the  genu  inferius, 


OCCIPITO-PARIETAL   SULCUS 


57 


in  the  lower  part  of  the  central  sulcus;  it  is  in  line  with  the  in- 
ferior frontal  sulcus  and  marks  the  lower  limit  of  the  arm  area 
and  the  upper  limit  of  the  face  area. 


go. 


6    t  o.S- 


The  Occipito-parietal  Sulcus  {Sulcus  occipito-parietalis) . — 
If  the  line  on  the  skull  locating  the  posterior  limb  of  the  lateral 
cerebral  fissure  be  extended  back  to  the  sagittal  meridian  its 
posterior  end  marks  the  location  of  the  occipito-parietal  sulcus. 
The  sulcus  is  located  one-sixth  of  an  inch  above  the  lambda  in 


58  THE    CEREBRUM 

the  adult,  and  is  from  one  and  a  half  to  two  inches  above  the 
occipital  pole.  The  greater  part  of  the  occipito-parietal  sulcus 
is  situated  on  the  medial  surface  of  the  cerebral  hemisphere, 
hence,  it  is  divided  into  an  internal  part  and  an  external  part 
which  are  continuous  through  the  supero-medial  border  (Figs. 
20,  26  and  34).  To  the  extent  of  its  depth,  which  is  about  one 
inch,  the  external  occipito-parietal  sulcus  separates  the  occipital 
from  the  parietal  lobe  on  the  convex  surface  of  the  hemisphere. 
Cunningham  considers  the  occipito-parietal  sulcus  a  true  fissure 
because  in  the  embryo  it  produces  a  ventricular  eminence, 
though  it  disappears  during  development.^ 

LOBES  AND  GYRI  OF  THE  CONVEX  SURFACE 

I.  The  frontal  lobe  {lohus  frontalis)  comprises  the  anterior 
polar  region  of  the  hemisphere  and  forms  a  part  of  all  three  sur- 
faces (Figs.  26,  31  and  34).  On  the  convex  surface,  it  extends 
as  far  back  as  the  central  sulcus  and  the  lateral  cerebral  fissure; 
on  the  basal  surface,  it  is  bounded  behind  by  the  stem  of  the 
lateral  cerebral  fissure  and  the  anterior  perforated  spot;  and  it  is 
limited  posteriorly  by  the  sulcus  cinguli  and  sulcus  parol- 
factorius  anterior  on  the  medial  surface  of  the  cerebral 
hemisphere. 

On  the  convex  surface,  the  frontal  lobe  has  the  following  sulci 
and  gyri  (Figs.  27  and  28): 

Superior  precentral  (s.  praecentralis  superior) 
Inferior  precentral  (s.  praecentralis  inferior) 
Superior  frontal  (s.  frontalis  superior) 
Inferior  frontal  (s.  frontalis  inferior) 
Middle  frontal  (s.  frontalis  medius) 
Paramedial  (s.  paramedialis) . 


Sulci    < 


Gyri 


Anterior  central  (g.  centralis  anterior) 
Superior  frontal  (g.  frontalis  superior) 
Middle  frontal  (g.  frontalis  medius) 
Inferior  frontal  (g.  frontalis  inferior). 


"^  The  name  of  this  sulcus  is  written  "occipito-parietal"  rather  than  "parieto- 
occipital;" this  is  a  simpler  word  to  pronounce  as  it  avoids  having  "oocc"lm 
the  middle  of  it. 


FRONTAL   GYRI  59 

The  precentral  sulci  (Fig.  27)  are  parallel  with  the  central 
sulcus  and  are  located  about  a  half  inch  in  front  of  it,  the  lower 
end  of  the  inferior  precentral  being  insinuated  between  the 
central  sulcus  and  the  ascending  ramus  of  the  lateral  fissure  of 
the  cerebrum.  They  form  the  anterior  boundary  of  the  anterior 
central  gyrus.  The  superior  frontal  sulcus  and  the  inferior 
frontal  sulcus  are  respectively  continuous  with  the  corresponding 
precentral  sulcus  from  which  they  trend  downward  and  forward 
parallel  with  the  supero-medial  border  of  the  hemisphere. 
They  separate  from  each  other  three  gyri  of  nearly  equal  width, 
viz.,  the  superior,  middle  and  inferior  frontal  gyri  (Fig.  24). 

The  superior  frontal  gyrus  is  incompletely  divided  in  the 
human  brain  by.  an  interrupted  sulcus,  called  the  sulcus  para- 
medians (Fig.  27)  which  is  located  near  the  supero-medial  border 
of  the  hemisphere  and  is  said  by  Cunningham  to  be  better  devel- 
oped in  the  higher  types  of  the  human  race  and  to  be  rare  in  the 
higher  apes. 

A  series  of  shallow  furrows,  described  by  Eberstaller  as  the 
middle  frontal  sulcus  {s.  frontalis  medius,  Fig.  27)  partially  sub- 
divides the  middle  frontal  gyrus  into  an  upper  and  a  lower  part. 
The  middle  frontal  sulcus,  not  found  below  the  anthropoid  apes 
(Cunningham),  is  best  marked  anteriorly  and,  at  the  super- 
ciliary border  of  the  hemisphere,  bifurcates  and  forms  a  hori- 
zontal furrow,  the  fronto-marginal  sulcus.  The  posterior  end, 
the  foot,  of  the  middle  frontal  gyrus,  like  that  of  the  superior 
and  inferior  frontal,  lies  in  the  psychic-motor  zone  of  the  brain. 
It  contains  the  writing  center  (Gordinier)  in  the  left  hemisphere 
of  right-handed  people. 

The  inferior  frontal  gyrus  is  highly  developed  in  the  human 
brain,  especially  in  the  left  hemisphere  of  right-handed  people. 
It  is  deeply  cleft  along  its  lower  border  by  the  anterior  ascending 
and  anterior  horizontal  rami  of  the  lateral  fissure  of  the  cerebrum 
and  is  thus  divided  into  a  pars  orbitalis,  situated  below  the 
anterior  horizontal  ramus,  a  pars  triangularis,  inclosed  between 
the  anterior  horizontal  and  ascending  rami,  and  a  pars  basilaris, 
located  between  the  anterior  ascending  ramus  of  the  lateral 
fissure  and  the  inferior  precentral  sulcus.     The  pars  basilaris 


6o 


THE    CEREBRUM 


constitutes  the  foot  of  the  inferior  frontal  gyrus  and  is  continu- 
ous with  the  gyrus  centralis  anterior;  on  the  left  side  it  contains 
the  speech  center.  The  pars  basilaris  is  often  divided  into  an 
anterior  and  posterior  part  by  the  sulcus  diagonalis;  the  pars 

.2  :3  3-5  j3  o 
bo  •  M+l.i5  "" 

^  S^S  .0.0 

dJ    5  W*  D  CIS     . 

S3;2      ^-^--^^ 
Oh   2  3    .  tn  y  w 

•-3     M  S  O  cS       rt 

o  ^  :s  «  c  g  a 

r-l       n    03*"    (1)    E-r! 


(U  ^  s  «  c  S 

^    .3     8J '-  v-- 
rs    «;  c!  w  vj   ^  (u 


«  o    .   •  2 
o  .2 £..^-2  o 


rt  ^ 


=^   s  u  bi     d  i: 
^  -H-^--^  ffi  v: « 


•-    *  ,-;M 


u,  "    CO    O      . 

«»   "2    ^§^« 


C5     £  w  c3  ri';3  )-!  i^ 


03    CO  .t;  ,7:    O  ^-  ^ 


triangularis  is  deeply  indented  from  above  by  a  branch  of  the 
inferior  frontal  sulcus,  called  the  sulcus  radiatus. 

The  anterior  portions  of  the  superior  middle  and  inferior 
frontal  gyri  comprise  a  psychic  center,  center  of  attention, 
volition,  inhibition,  etc.,  "of  abstract  concept"  (Mills). 


PARIETAL   LOBE  6 1 

The  anterior  central  gyrus  (g.  centralis  anterior)  lies  between 
the  precentral  sulci  and  the  central  sulcus.  It  is  joined  to  the 
posterior  central  gyrus  by  the  paracentral  lobule,  above  the 
central  sulcus,  and  by  the  fronto-parietal  part  of  the  operculum, 
below  it.  The  anterior  central  gyrus,  together  with  the  para- 
central lobule  constitutes  the  emissive  motor  zone  of  the  human 
cerebrum. 

2.  The  parietal  lobe  (lobus  parietalis)  is  situated  behind 
the  central  sulcus  and  above  the  posterior  limb  of  the  lateral 
fissure  of  the  cerebrum  (Figs.  26  and  34).  From  the  curve  near 
the  posterior  end  of  the  latter  to  the  occipito-parietal  sulcus  the 
lobe  is  separated  from  the  temporal,  below,  and  the  occipital, 
behind,  by  an  imaginary  line.  This  imaginary  line  runs  back- 
ward parallel  with  the  infero-lateral  border  of  the  hemisphere 
to  the  boundary  of  the  occipital  lobe;  and  then,  obliquely  up- 
ward toward  the  supero-medial  border  in  a  line  drawn  from  the 
preoccipital  notch  to  the  occipito-parietal  sulcus.  Extending 
over  the  supero-medial  border,  the  lobe  on  the  medial  surface 
is  inclosed  between  the  occipito-parietal  sulcus  behind  and  the 
marginal  part  of  the  sulcus  cinguli  in  front,  and  is  bounded 
antero-inferiorly  by  the  subparietal  sulcus. 

On  the  convex  surface  of  the  hemisphere  the  parietal  lobe 
possesses  the  following  sulci  and  gyri  (Figs.  27  and  28). 

Interparietal  (s.  interparietalis)  four  parts — 
Inferior  post-central  (s.  post-centralis  inferior) 
Superior  post-central  (s.  post-centralis  superior) 
Horizontal  limb  (ramus  horizontalis) 
Occipital  limb  (ramus  occipitalis) . 


Sulci  { 


Gyri 


Upturned  ends  of 
Lateral  fissure  (f.  cerebri  lateralis) 
Superior  temporal  sulcus  (s.  temporalis  superior) 
Middle  temporal  sulcus  (s.  temporalis  medius). 

Posterior  central  (g.  centralis  posterior) 
Superior  parietal  lobule  (1.  parietalis  superior) 
Inferior  parietal  lobule  (1.  parietalis  inferior) 

Supramarginal  (g.  supramarginalis) 

Angular  (g.  angularis) 

Post-parietal  (g.  post-parietalis). 


62  THE    CEREBRUM 

The  interparietal  sulcus  (Figs.  20  and  27)  is  the  only  one 
belonging  to  the  parietal  lobe.  The  inferior  and  superior  post- 
central sulci,  constituting  its  anterior  parts,  are  parallel  with  the 
central  sulcus  and  are  located  a  half  or  three-quarters  of  an  inch 
behind  it,  separated  from  the  central  sulcus  by  the  gyrus 
centralis  posterior.  The  post-central  sulci  are  often  not  con- 
tinuous. The  inferior  is  about  twice  the  length  of  the  superior, 
in  this  resembling  the  central  sulcus,  and  usually  it  is  joined  at 
its  upper  end  to  the  horizontal  limb  of  the  interparietal  sulcus. 
The  horizontal  part  of  the  sulcus  lies  about  an  inch  below  the 
supero-medial  border  of  the  hemisphere  with  which  it  is 
parallel;  it  separates  the  superior  parietal  lobule  from  the  in- 
ferior parietal  lobule  and  is  continued  as  ramus  occipitalis  into 
the  occipital  lobe  where  it  bifurcates.  The  horizontal  part  of 
this  sulcus  has  one  superior  and  two  inferior  rami;  the  trans- 
verse parietal  ramus  runs  toward  the  supero-medial  border, 
bisecting  the  superior  parietal  lobule;  the  intermediate  rami 
descend,  the  first  is  opposite  the  transverse  parietal  and  be- 
tween the  up-turned  ends  of  the  lateral  fissure  and  first  tem- 
poral sulcus,  the  second  intermediate  ramus  descends  behind 
the  first  temporal  sulcus. 

The  posterior  central  gjnnis  reaches  from  the  posterior  limb 
of  the  lateral  fissure  upward  and  backward,  between  the  central 
and  post-central  sulci,  to  the  longitudinal  fissure  of  the  cere- 
brum (Fig.  28).  It  is  joined  to  the  anterior-central  gyrus 
around  the  ends  of  the  central  sulcus  by  superficial  annectant 
gyri  (gyri  transitivi)  and  sometimes  is  connected  with  it  by  a 
buried  gyrus  {g.  profundus  transitivus)  which,  deeply,  separates 
the  superior  from  the  inferior  part  of  the  central  sulcus.  The 
annectant  gyrus  which  closes  the  central  sulcus  superiorly  and 
links  together  the  central  gyri  is  the  paracentral  lobule  {lohulus 
paracentralis) ;  the  fronto-parietal  part  of  the  operculum  joins 
them  below  the  central  sulcus.  The  posterior  central  gyrus 
and  paracentral  lobule  constitute  the  receptive  area  of  common 
sensation,  the  somcesthetic  area,  so  far  as  it  extends  on  the  convex 
surface. 

The  superior  parietal  lobule  (Figs.   20  and  28)  forms  the 


SUPERIOR  PARIETAL  LOBULE 


63 


supero-medial  border  of  the  hemisphere  from  the  superior  post- 
central to  the  occipito-parietal  sulcus.  It  is  separated  from  the 
inferior  parietal  lobule  by  the  horizontal  part  of  the  interparietal 


sulcus;  posteriorly,  it  is  joined  to  the  occipital  lobe  by  a  curved 
annectant  gyrus,  called  the  arcus  occipito-parietalis,  which  closes 
the  superior  end  of  the  occipito-parietal  sulcus;  and,  over  the 
supero-medial  border,  it  is  continuous  with  the  praecuneus  of  the 


64 


THE    CEREBRUM 


medial  surface.     In  the  praecuneus  and  the  superior  parietal 
lobule  Mills  locates  the  stereognostic  center  (Figs.  76  and  77). 
The  Inferior  Parietal  Lobule. — The  inferior  parietal  lobule  is 


incompletely  divided  into  two  or  three  gyri.  Named  from 
before  backward  they  are  as  follows:  The  supramarginal,  the 
angular  and  the  post-parietal  (Figs.  20  and  28). 


INFERIOR   PARIETAL    LOBULE  65 

The  supramarginal  gyrus  arches  over  and  closes  the  upturned 
end  of  the  posterior  ramus  of  the  lateral  fissure  of  the  cerebrum 
(Fig.  28).  The  anterior  segment  of  the  arch  is  continuous  with 
the  posterior  central  gyrus ,  the  posterior  segment  of  the  arch 
fuses  with  the  angular  gyrus,  behind,  and  the  superior  temporal 
gyrus,  below.  The  supramarginal  gyrus  is  partially  separated 
from  the  angular  gyrus  by  the  sulcus  intermedins  primus.  This 
gyrus  belongs  in  the  psychic  sensory  area,  probably  containing 
the  center  of  the  muscle  sense  (Fig.  76). 

The  angular  gyrus  is  behind  the  supramarginal  gyrus  and 
between  the  first  and  second  intermediate  rami  of  the  inter- 
parietal sulcus.  It  forms  an  arch  over  the  end  of  the  superior 
temporal  sulcus  (Figs.  20  and  28).  The  angular  arch  is  in 
direct  continuity  with  the  superior  and  middle  temporal  gyri  and 
the  posterior  segment  of  it  is  continuous  with  the  post-parietal 
gyrus  when  that  gyrus  is  present. 

The  post-parietal  g3TUS  is  present  only  when  the  middle 
temporal  sulcus  bends  upward  and  terminates  in  the  parietal 
lobe;  in  which  case  this  gyrus  curves  over  and  closes  that  sulcus 
(not  figured) .  It  connects  the  posterior  ends  of  the  inferior  and 
middle  temporal  gyri  and  also  blends  with  the  superior  occipital 
gyrus.  The  angular,  post-parietal  and  superior  occipital  gyri 
on  the  left  side,  according  to  Mills  and  others,  constitute  the 
center  for  visual  memories.  The  studies  of  A.  W.  Campbell  render 
it  probable  that  the  visual  cortex  does  not  extend  into  the 
parietal  lobe  of  man  at  all.  The  receptive  visual  center  for 
macular  vision  (vision  in  the  macula  lutea  of  the  retina)  is  like- 
wise located  in  the  angular  or  post-parietal  gyrus  by  Mills, 
but  it  is  probably  situated  on  the  medial  surface  of  the  occip- 
ital lobe;  unlike  the  memory  center,  this  is  present  in  both 
hemispheres. 

The  whole  parietal  lobe,  excepting  the  frontal  half  of  the 
posterior  central  gyrus,  lies  in  the  psychic  sensory  region. 

3.  Occipital  Lobe  (Lobus  occipitalis,  Figs.  20,  26,  28,  31 
and  34). — The  occipital  lobe  forms  the  posterior  pole  of  the  hemi- 
sphere. With  the  parietal  and  temporal  lobes  it  is  directly  con- 
tinuous, being  marked  off  from  them  by  an  imaginary  line 
S 


66  THE    CEREBRUM 

drawn  from  the  preoccipital  notch  to  the  occipito-parietal  sulcus. 
This  sulcus,  on  the  convex  surface,  bounds  it  to  the  extent  of 
about  an  inch;  rarely,  the  anterior  and  transverse  occipital  sulci 
bound  it  in  front.  On  the  medial  and  basal  surfaces  of  the  hemi- 
sphere the  occipital  lobe  extends  from  the  occipito-parietal  sul- 
cus and  anterior  calcarine  fissure  to  the  preoccipital  notch,  and 
is  separated  from  the  temporal  lobe  on  the  basal  surface  by  an 
imaginary  line  drawn  from  this  notch  toward  the  posterior  end 
of  the  corpus  callosum,  to  the  isthmus  of  the  limbic  lobe.  The 
occipital  lobe  has  the  form  of  a  triangular  pyramid  whose  borders 
are  the  supero-medial,  the  infero-lateral  and  the  medial  occipital 
borders  of  the  cerebral  hemisphere.  Those  borders  meet  at  its 
apex,  the  occipital  pole. 

The  followers  of  Eberstaller  almost  limit  the  occipital  lobe 
to  the  tentorial  and  medial  surfaces  of  the  hemisphere;  they 
describe  the  collateral  fissure  as  the  infero-lateral  boundary 
on  the  tentorial  surface.  This  extends  the  temporal  lobe  to  the 
occipital  pole. 

The  occipital  lobe  is  somewhat  retrogressive  in  man,  though 
present  only  in  apes  and  men  (Cunningham).  It  makes  its 
appearance  at  the  fourth  month  in  utero,  and  is  distinctly  out- 
lined by  fissures  on  all  three  surfaces  at  the  sixth  month,  when  it 
resembles  the  same  lobe  in  the  adult  ape's  brain  (Cunningham 
Memoirs).  After  the  sixth  month  the  fissural  boundaries 
largely  disappear  from  the  human  brain  on  the  convex  and  basal 
surfaces;  hence,  the  artificial  boundaries  in  the  adult.  Its 
retrogressive  character  probably  accounts  for  the  great  varia- 
bility in  the  sulci  and  gyri  of  the  occipital  lobe.  On  the  convex 
surface  they  are  usually  as  follows; 

(Ramus  occipitalis  of  interparietal  sulcus 
Transverse  occipital  (s.  occipitalis  transversus) 
Lateral  occipital  (ss.  occipitales  laterales). 

„     .  f  Superior  occipital  (gg.  occipitales  superiores) 
I  Lateral  occipital  (gg.  occipitales  laterales). 

The  lateral  occipital  sulcus  is  the  only  one  properly  belonging 
to  the  convex  surface  of  the  occipital  lobe  (sometimes  there  are 
two  of  them).     It  divides  that  surface  almost  equally  into  a 


OCCIPITAL   SULCI  AND    GYRI  67 

superior  and  lateral  gyrus,  both  of  which  may  be  double.  The 
sulcus  begins  near  the  supero-medial  border.  It  follows  a 
meridian  which  is  nearly  parallel  with  the  infero-lateral  border 
of  the  lobe  and  runs  forward,  often  presenting  one  interruption, 
to  the  occipito-temporal  boundary  line.  Posteriorly,  it  may 
bifurcate  and  form  the  short  lunate  sulcus  {s.  simialis),  which 
represents  the  affenspalte  of  the  ape  (ElHot  Smith).  When  the 
lateral  occipital  sulcus  is  double  there  are  two  lateral  gyri 
(Figs.  20,  27  and  28). 

The  occipital  limb  of  the  interparietal  sulcus  descends  in 
the  occipital  lobe  a  variable  distance  (Fig.  20).  It  is  not  always 
continuous  with  the  horizontal  limb.  Running  about  an  inch 
from  the  supero-medial  border  of  the  hemisphere,  it  passes  the 
occipito-parietal  sulcus,  from  which  it  is  separated  by  the  arcus 
occipito-parietalis,  and  bifurcates  in  the  superior  occipital 
gyrus  into  two  more  or  less  oblique  branches,  constituting  the 
transverse  occipital  siilcus.  The  medial  end  of  the  transverse 
sulcus  may  or  may  not  cut  the  supero-medial  border  of  the  lobe; 
the  lateral  branch  sometimes  descends  along  the  occipito- 
temporal boundary.  If  the  transverse  and  lateral  sulci  fail 
to  reach  the  longitudinal  fissure,  a  perpendicular  gyrus  forms 
the  supero-medial  border  of  the  occipital  lobe  called  the 
gyrus  descendens. 

The  lateral  occipital  gyrus  (Figs.  20  and  28)  lies  below  the 
lateral  occipital  sulcus  and  extends  from  the  occipital  pole 
forward  along  the  infero-lateral  border  of  the  hemisphere  to 
the  preoccipital  notch.  Sometimes  it  is  divided  into  two  lateral 
gyri  by  an  inferior  lateral  sulcus.  It  is  continuous  with  the 
inferior  temporal  gyrus,  except  rarely,  when  the  two  are  sepa- 
rated by  the  anterior  occipital  sulcus. 

The  superior  occipital  gyrus  forms  the  upper  half  of  the 
convex  surface  of  the  lobe  (Figs.  20  and  28).  It  is  incompletely 
separated  from  the  lateral  occipital  gyrus  by  the  lateral  occipital 
sulcus  and  is  often  divided  into  two  gyri.  It  is  continuous  with 
the  post-parietal  gyrus  around  the  lateral  end  of  the  transverse 
occipital  sulcus;  and,  around  the  medial  end  of  that  sulcus,  it 
is  joined  to  the  superior  parietal  lobule  by  the  arcus  occipito- 


68  THE    CEREBRUM 

parieatlis.  The  latter  is  a  sharply  curved  annectant  gyrus 
which  bounds  the  occipito-parietal  sulcus.  When  the  middle 
temporal  sulcus  does  not  turn  upward  at  its  posterior  end  and 
terminate  in  the  parietal  lobe,  the  superior  occipital  gyrus  is 
continuous  in  front  with  the  middle  temporal  and  angular  gyri. 
As  already  mentioned,  the  superior  occipital  gyrus,  according 
to  Mills,  belongs  to  the  center  for  visual  memories. 

4.  The  temporal  lobe  ilohus  temporalis,  Figs.  20,  26,  27,  28, 
30  and  31)  is  that  part  of  the  cerebral  hemisphere  behind  the 
main  stem  and  below  the  posterior  limb  of  the  lateral  cerebral 
fissure.  It  rests  in  the  middle  fossa  of  the  skull;  forms  the 
temporal  pole  of  the  hemisphere;  and  is  continuous  posteriorly 
with  the  occipital  and  parietal  lobes,  from  which  it  is  marked 
off  only  by  the  imaginary  lines  already  described.  On  the  basal 
surface  of  the  hemisphere,  the  temporal  lobe  along  its  medial 
border  is  separated  from  the  limbic  lobe  by  the  collateral  fissure 
and  by  a  short  furrow,  which  is  shallow  in  the  adult  human 
brain,  called  the  sulcus  ecto-rhinalis.  The  temporal  lobe  is 
attached  to  the  hemisphere  posteriorly  and  medially;  but  it 
presents  three  free  surfaces — a  superior,  a  lateral  and  an  in- 
ferior— which  meet  at  the  anterior  point,  called  the  temporal 
pole.  The  polar  region  is  incompletely  separated  from  the 
temporal  gyri  by  the  crescentic  anterior  temporal  sulcus,  when 
that  is  present. 

The  superior  surface  of  the  temporal  lobe  forms  the  inferior 
wall  of  the  lateral  cerebral  fissure  (Fig.  30).  It  looks  somewhat 
medianward  toward  the  island  and  constitutes  the  temporal  part 
of  the  operculum.  It  presents  a  long  oblique  gyrus  and  two 
or  three  transverse  gyri,  separated  by  shallow  grooves.  The 
long  oblique  gyrus  is  adjacent  to  the  gyrus  longus  of  the  island, 
the  sulcus  circularis  intervening  between  them;  it  is  continuous 
anteriorly  with  the  superior  temporal  gyrus;  posteriorly  it  re- 
cedes from  the  convex  surface  and  is  connected  with  it  only  by 
the  transverse  temporal  gyri  of  Heschl  (gyri  temporales  trans- 
versi),  which  abut  against  the  oblique  gyrus  at  an  acute  angle. 
These  transverse  gyri  belong  to  the  receptive  auditory  center 
(Figs.  38,  46,  47  and  74). 


TEMPORAL  LOBE  69 

The  external  surface  of  the  temporal  lobe  presents  the  fol- 
lowing sulci  and  gyri  (Figs.  27  and  28): 


Sulci  < 


Superior  temporal  (s.  temporalis  superior) 
Middle  temporal  (s.  temporalis  medius) 
Inferior  temporal  (s,  temporalis  inferior).     This  is  really 
on  the  inferior  surface  of  the  lobe. 


(Superior  temporal  (g.  temporalis  superior) 
Middle  temporal  (g.  temporalis  medius) 
Inferior  temporal  (g.  temporalis  inferior). 

The  superior  temporal  and  middle  temporal  sulci  (Fig.  27)  di- 
vide the  external  surface  into  three  nearly  equal  gyri;  they  run 
parallel  with  each  other,  with  the  infero-lateral  border  and  with 
the  lateral  cerebral  fissure.  The  superior  temporal  sulcus,  Uke 
the  lateral  fissure,  bends  upward  at  its  posterior  extremity; 
as  sulcus  angularis,  it  terminates  in  the  concavity  of  the  angular 
gyrus.  The  middle  temporal  sulcus  is  usually  an  interrupted 
one.  It  may  present  an  upward  curve  at  its  posterior  end  which 
is  bounded  and  closed  by  the  post-parietal  gyrus;  or  it  may  con- 
tinue in  its  original  direction  toward  the  occipital  lobe. 

The  inferior  temporal  sulcus,  situated  in  the  tentorial  area  of 
the  basal  surface,  runs  interruptedly  close  to  the  infero-lateral 
border  of  the  hemisphere  and  parallel  with  it  (Fig.  31).  It  sepa- 
rates the  inferior  temporal  gyrus  from  the  fusiform  gyrus. 

The  superior  temporal,  the  middle  temporal  and  the  inferior 
temporal  gyri  are  of  nearly  equal  width  (Figs.  28  and  31). 
They  fuse  with  one  another  and  with  the  fusiform  gyrus  at  the 
temporal  pole,  when  anterior  temporal  sulcus  is  absent.  The 
superior  temporal  gyrus  is  continuous  with  the  supramarginal 
and  angular  gyri,  posteriorly:  in  its  third  and  fourth  fifths  and 
in  the  transverse  temporal  gyri  is  the  receptive  auditory  center 
(Barker). 

The  middle  temporal  gyrus  fuses  at  its  posterior  end  with 
the  angular  gyrus  and  either  with  the  post-parietal  or  the 
superior  occipital.  Along  the  superior  temporal  sulcus,  in  the 
middle  two-fourths  of  the  superior  and  middle  temporal  gyri 
is  the  center  for  auditory  memories,  the  psychic  auditory  center. 


70  THE   CEREBRUM 

This  center  is  in  the  left  hemisphere  of  right-handed  people 
(Figs.  74  and  76). 

The  inferior  temporal  gyrus  forms  the  infero-lateral  border 
of  the  hemisphere  (Figs.  28  and  31).  It  is  continuous  with  the 
lateral  occipital  gyrus  and  sometimes,  also,  with  the  superior 
occipital  and  post-parietal  gyri.  If  this  gyrus  and  the  lower 
half  of  the  middle  temporal  gyrus  be  divided  into  four  equal 
parts,  each  fourth,  according  to  Mills,  belongs  to  a  definite 
center.  From  behind  forward  they  are  the  center  of  orienta- 
tion; the  center  of  equilibration  {?);  the  naming  center;  and,  in  the 
anterior  fourth  and  the  pole  of  the  temporal  lobe,  the  center  of 
intonation  (Fig.  76). 

5.  The  island  {insula,  ReiH)  is  also  called  the  central  lobe 
(Figs.  30,  31,  38  and  47).  It  is  situated  in  the  medial  wall  of 
the  lateral  fissure  of  the  cerebrum,  between  the  frontal,  parietal 
and  temporal  lobes,  whose  growth,  after  the  fifth  month  in 
utero,  gradually  covers  it  over.  At  the  end  of  the  first  year  of 
extrauterine  life  it  is  entirely  concealed  by  temporal,  parietal, 
and  frontal  parts  of  the  operculum.  The  island  is  thus  sepa- 
rated from  the  general  surface  of  the  cerebral  hemisphere  by 
a  distance  of  half  or  three-quarters  of  an  inch.  It  is  triangular 
in  shape.  Its  apex  is  directed  downward  and  forward  toward 
the  fossa  lateralis  cerebri,  and  is  called  the  pole  {polus  insulce). 
If  the  lips  of  the  lateral  fissure  be  widely  separated,  the  stilcus 
circularis  insulae  may  be  seen  separating  the  island  from  the 
frontal,  parietal  and  temporal  lobes  (Figs.  30,  31  and  47). 
The  circular  sulcus  is  lacking  only  at  the  antero-inferior  part, 
at  the  pole,  where  the  cortex  of  the  island  is  continuous  with 
that  of  the  posterior  orbital  gyrus  and  with  the  anterior  per- 
forated substance,  and  is  on  the  same  level  as  the  orbital  area 
of  the  basal  surface.  The  imaginary  Hne  separating  the  an- 
terior perforated  substance  from  the  island  is  called  the  threshold 
of  the  island  {limen  insulce) . 

In  the  island  there  is  one  named  sulcus  and  four  to  six  gyri 
which  have  a  radial  or  fan-like  grouping  (Fig.  25) : 

Sulcus    {  Central  of  the  island  (s.  centralis  insulae). 
P     .    f  Short  (gyri  breves),  three  or  four  of  them. 
\  Long  (gyrus  longus — furcalis). 


GYRI   OF   ISLAND  7 1 

The  sulcus  centralis  insulce  begins  at  the  apex,  or  pole,  of  the 
island  and  runs  obliquely  upward  and  backward  dividing  the 
lobe  into  two  lobules  (Fig.  30).  It  is  in  the  same  transverse 
plane  as  the  central  sulcus  (of  Rolando).  In  front  of  it,  is  the 
precentral  lobule  composed  of  the  short  gyri  and  continuous 
with  the  frontal  lobe;  the  post-central  lobule  lies  behind  it  and 
is  in  continuity  with  the  parietal,  temporal  and  limbic  lobes. 

The  gjrri  breves  inuslae,  three  or  four  in  number,  are  separated 
by  shallow  furrows  Vhich  diverge  upward  and  backward  from 
the  smooth  apex  of  the  precentral  lobule  (Fig.  30).  They  are 
joined  to  the  orbital  operculum  by  a  short  annectant  gyrus 
{gyrus  iransversus  insulce  of  Eherstaller)  which  extends  from  the 
apex  around  the  lower  end  of  the  anterior  circular  sulcus.  Their 
connection  under  the  circular  sulcus  with  the  foot  of  the  in- 
ferior frontal  gyrus  suggests  a  participation  in  the  speech  center, 
and  they  are  figured  by  Mills  in  that  center.  However,  the 
paraphasia  which  results  from  lesions  in  the  short  gyri  may  be 
due  to  the  involvement  of  an  association  tract  of  fibers  running 
underneath  them. 

Gyrus  Longus  (Furcalis)  (Fig.  30). — It  lies  behind  the  central 
sulcus  of  the  island  and  trends  obliquel}'-  backward  and  upward. 
Posteriorly,  it  bifurcates  for  a  short  distance  forming  two  short 
branches  which  are  continuous  under  the  circular  sulcus  with  the 
parietal  lobe;  it  fuses  with  the  temporal  lobe  and  the  gyrus 
hippocampi  of  the  limbic  lobe,  inferiorly. 

The  olfactory  lobe  and  the  limbic  lobe,  comprising  the  rhinen- 
cephalon  and  a  part  of  the  neopallium,  also  belong  to  the 
cerebral  hemisphere;  but  no  part  of  either  can  be  seen  on  the 
convex  surface  (Figs.  18,  21  and  34), 

THE  BASE  OF  THE  FORE-BRAIN 

The  basal  or  inferior  surface  of  the  fore-brain  comprises  the 
inferior  surface,  first,  of  the  end-brain,  including  the  pars  optica 
hypothalami  and  the  cerebral  hemispheres;  and,  second,  of  the 
inter-brain,  which  embraces  the  pars  mammillaris  hypothalami. 
It  is  completely  exposed  only  when  a  section  is  made  through  the 


72  THE    CFREBRUM 

mid-brain  and  the  rhombencephalon  removed  (Figs.  21  and  31). 
This  should  now  be  done  with  a  thin,  moistened  brain-knife. 
Make  the  section  from  before  backward  and  upward,  at  a  right 
angle  to  the  axis  of  the  mid-brain.  Now  notice,  first,  the  section 
of  the  mid-brain  and,  just  anterior  to  that,  the  median  struc- 
tures of  the  fore-brain,  occupying  the  center  of  the  field;  and, 
second,  the  surrounding  inferior  surface  of  the  cerebral  hemi- 
spheres.    The  latter  form  the  very  large  peripheral  zone. 

The  base  of  the  cerebral  hemisphere  extends  from  the  frontal 
to  the  occipital  pole.  In  front  it  is  composed  of  the  orbital  area 
bounded  by  the  medial  orbital  and  superciliary  borders;  and, 
posteriorly,  is  made  up  of  the  tentorial  area,  which  is  boui>ded, 
laterally,  by  the  infero-lateral  border,  and,  medially,  by  the 
chorioidal  fissure  and  the  medial  occipital  margin  of  the 
hemisphere  (Fig.  31).  The  orbital  area  embraces  the  inferior 
surface  of  the  frontal  lobe  and  of  the  island,  and  the  whole  ol- 
factory lobe;  while  the  inferior  surface  of  the  temporal  and 
occipital  lobes,  and  the  gyrus  hippocampi  and  fascia  dentata 
of  the  limbic  lobe  are  included  in  the  tentorial  area. 

Frontal  Lobe,  Inferior  Surface  (Fig.  31). — The  inferior  surface 
of  the  frontal  lobe,  resting  on  the  orbital  plate  of  the  frontal 
bone,  is  often  called  the  orbital  lobe.  It  is  separated  from  its 
fellow  by  the  longitudinal  fissure  of  the  cerebrum,  and  is  bounded 
behind  by  the  lateral  fossa  and  lateral  fissure  of  the  cerebrum, 
overlapped  by  the  temporal  lobe.  More  accurately,  the  pos- 
terior boundary  is  the  anterior  perforated  substance  and  the 
anterior  part  of  the  circular  sulcus.  The  orbital  lobe  is  con- 
cave transversely  and  is  divided  by  the  triradiate  or  H-shaped 
sulcus  orbitaliSy  made  up  of  the  medial  orbital,  the  transverse 
orbital  and  the  lateral  orbital  sulci;  and  by  the  olfactory  sulcus, 
which  is  close  to  the  longitudinal  fissure  and  nearly  parallel  with 
it.     Five  gyri  are  thus  formed: 


Gyri 


Straight  (g.  rectus) 

Medial  orbital  (g.  orbitalis  medialis) 

Lateral  orbital  (g.  orbitalis  lateralis),  not  constant 

Anterior  orbital  (g.  orbitalis  anterior) 

Posterior  orbital  (g.  orbitalis  posterior). 


STRAIGHT  AND   ORBITAL   GYRI  73 

The  gyrus  rectus  (Fig.  31)  forms  the  medial  border  of  this 
surface.  It  is  separated  from  the  medial  orbital  gyrus  by  the 
sulcus  olfactorius  in  which  lie  the  olfactory  bulb  and  tract. 
Over  on  the  medial  surface  it  forms  part  of  a  marginal  gyrus 
and  it  joins  the  superior  frontal  at  the  frontal  pole.  Pos- 
teriorly the  gyrus  rectus  is  separated  from  the  parolfactory  area 
(of  Broca)  by  a  slight  furrow,  the  anterior  parolfactory  sulcus. 

The  medial  orbital  gyrus  lies  between  the  sulcus  of  the  same 
name  and  the  sulcus  olfactorius  (Fig.  31).  It  extends  from  the 
frontal  pole  to  the  anterior  perforated  substance  and  the  island. 
The  anterior  and  posterior  orbital  gyri  lie  within  the  H-shaped 
orbital  sulcus  separated  from  each  other  by  the  transverse 
orbital  sulcus.  The  former  is  continuous  with  the  frontal 
gyri  at  the  superciKary  border;  the  latter  is  only  partially 
separated,  behind,  from  the  island  by  the  anterior  circular  sulcus ; 
the  posterior  orbital  gyrus  is  likewise  continuous  with  the  pos- 
terior  end  of  the  lateral  orbital  gyrus  and  with  the  orbital 
portion  of  the  inferior  frontal.  The  lateral  orbital  gyrus,  which 
is  a  distinct  gyrus  only  when  the  lateral  orbital  sulcus  is  long, 
is  situated  lateral  to  the  H-shaped  sulcus.  It  is  continuous 
with  both  middle  and  inferior  frontal  gyri  at  the  superciliary 
border  of  the  hemisphere. 

The  Island  (of  Reil).  Inferior  Surface  (Fig.  31). — If  the  an- 
terior part  of  the  temporal  lobe  be  removed,  the  under  surface 
of  the  island  (insula)  is  brought  into  view.  The  circular  sulcus 
bounds  it  on  two  sides  and  separates  it  from  the  posterior  orbital 
gyrus,  in  front;  and  from  the  temporal  lobe,  behind.  Laterally 
it  is  separated  from  the  frontal  and  the  parietal  parts  of  the 
operculum  by  an  antero-posterior  cleft  continuous  with  the 
lateral  cerebral  fissure. 

The  insula  is  continuous  with  the  anterior  perforated  sub- 
stance, and  the  area  of  transition  from  one  to  the  other  is  called 
the  threshold,  or  limen  insulce  (Fig.  31). 

Rhinencephalon. — The  smelling  brain  belongs  to  the  basal 
surface.  It  is  retrogressive  in  man,  being  relatively  larger  and 
better  developed  at  the  fifth  month  in  utero  than  in  the  brain 
of  an  adult.     Many  connected  parts  make  it  up.     It  is  divided 


74 


THE   CEREBRUM 


.R.«^ 


Fig.  31. — Base  of  fore-brain  and  cut  surface  ot  mid-brain.  Right  temporal 
pole  cut  away,  to  show  inferior  surface  of  the  island.  (Original.) 
a.  Sulcus  parolf actorius  anterior,  b.  Sulcus  parolf actorius  posterior,  c.  Olfactory  bulb. 
d.  Olfactory  tract,  e.  Olfactory  striae,  f.  Area  parolfactoria.  g.  Trigonum  olfactor- 
ium.  h.  Substantia  perforata  anterior,  i.  Diagonal  gyrus,  or  band,  of  Broca,  continuous 
with' gyrus  subcallosus  (peduncle  of  corpus  callosum).  j.  Optic  chiasma.  k.  Optic  tract. 
1.  Tuber  cinereum.  m.  Infundibulum.  n.  Corpus  mammillare.  0.  Substantia  per- 
forata posterior,  p.  Aqueductus  cerebri,  q.  Quadrigeminal  colliculus.  r.  Corpus  pineale. 
s.   Splenium. 


OLFACTORY  LOBE  75 

into  two  embryonic  parts  by  the  sulcus  parolf actor ius  posterior. 
These  are  designated  as  the  pars  anterior  rhinencephali  and  the 
pars  posterior  rhinencephali.  The  pars  anterior  of  the  rhinen- 
cephalon,  the  olfactory  lobe,  embraces  the  olfactory  bulb,  tract, 
triangle,  the  medial  and  intermediate  striae  and  the  area  parol- 
factoria.  In  the  pars  posterior  rhinencephali  are  included  the 
anterior  perforated  substance,  the  gyrus  subcallosus,  gyrus 
diagonalis,  the  lateral  olfactory  stria,  the  limen  insulae,  the 
uncus  and  hippocampal  formation. 

Olfactory  Lobe  {Lobus  olfactorius) . — There  is  one  lobe  that  is 
studied  only  on  the  basal  surface  of  the  fore-brain.  That  is  the 
olfactory  lobe  (Fig.  31).  Being  the  pars  anterior  rhinencephali, 
it  comprises  six  connected  parts;  and  the  reason  for  calling  them 
the  olfactory  lobe  is  found  in  the  lower  animals  and  in  the  human 
embryo,  where  it  exists  as  a  prominent  hollow  process  of  the 
cerebral  hemisphere  (Figs.  17  and  18). 

In  the  horse,  ox,  sheep,  dog,  pig,  etc.,  the  olfactory  lobe  con- 
tains a  ventricle  continuous  through  the  intermediate  stria 
with  the  lateral  ventricle. 


Olfactory  Lobe 


Bulbus  olfactorious 
Tractus  olfactorius 
Trigonum  olfactorium 
Stria  medialis 
Stria  intermedia 
Area  parolfactoria. 


The  olfactory  bulb  {bulbus  olfactorius)  is  an  ovoid  mass  of 
brain  matter  about  12  mm.  (0.5  in.)  long,  4  mm.  (0.17  in.)  wide 
and  6  mm.  (0.25  in.)  in  vertical  diameter  (Fig.  31).  It  is 
lodged  in  the  olfactory  sulcus  of  the  frontal  lobe  and  rests  upon 
the  cribriform  plate  of  the  ethmoid  bone  through  which  it 
receives  the  twenty  or  thirty  olfactory  nerves.  The  center  of 
the  bulb  is  formed  by  a  gelatinous  core  derived  from  the  ependy- 
mal  lining  of  the  embryonic  ventricle.  The  gray  core  is  sur- 
rounded by  a  white  sheath  of  meduUated  fibers  running  longi- 
tudinally; posterior  to  the  bulb  these  fibers  enter  the  olfactory 
tract.  Five  layers  of  gray  substance  thicker  on  the  ventral 
side,  surround  the  white  sheath  and  constitute  the  surface  of 


76  THE   CEREBRUM 

the  bulb.  The  gray  substance  forms  the  terminal  nucleus  of 
the  olfactory  nerves  and  gives  origin  to  the  fibers  of  the  olfactory 
tract. 

Olfactory  Tract  (Tractus  olf actor ius) . — The  tract  is  triangular 
in  section,  slightly  more  than  2  cm.  long  and  2.5  mm.  in  width 
(Fig.  26).  It  is  partially  concealed  in  the  olfactory  sulcus  and 
is  composed  chiefly  of  the  medullated  axones  of  the  mitral  and 
brush  cells  in  the  bulb,  they  form  its  broad  basal  portion;  but 
its  narrow  dorsal  border  is  made  up  largely  of  gray  substance, 
called  the  cortex  of  the  olfactory  tract,  and  its  center  is  formed 
by  a  gelatinous  core  derived  from  the  ependyma  of  the  embryonic 
ventricle.  The  origin  of  the  olfactory  lobe,  as  a  hollow  divertic- 
ulum of  the  telencephalon,  explains  this  formation  of  bulb  and 
tract.  At  its  posterior  end  the  olfactory  tract  divides  into 
three  striae — lateral,  intermediate  and  medial,  two  of  which  are 
easily  seen.  These  strice  olfactorice  are  continuous  with  the 
three  angles  of  the  tract.  The  lateral  and  medial  striae  diverge 
and  inclose  the  olfactory  triangle  between  them. 

The  fibers  of  the  olfactory  tract  are  not  continued  through 
the  striae  as  they  appear  to  be;  they  terminate  in  the  cortex  of 
the  tract,  the  olfactory  triangle,  the  anterior  perforated  sub- 
stance and  the  septum  pellucidum,  whence  new  sets  of  fibers 
take  their  origin.  The  lateral  stria  {stria  olfactoria  lateralis) 
rising  from  the  olfactory  triangle,  courses  outward  and  back- 
ward and  terminates  in  the  uncus  at  the  anterior  extremity  of 
the  hippocampal  gyrus.  According  to  Retzius,  the  lateral 
olfactory  stria  terminates  in  the  rudimentary  gyri,  circum- 
amhiens  and  semilunaris,  which  form  the  anterior  end  of  the 
hippocampal  gyrus.  The  lateral  stria  bounds  on  the  outer  side 
the  anterior  perforated  space.  The  medial  stria  {stria  medialis) 
bends  sharply  inward,  toward  the  median  line,  and  runs  between 
the  triangle  and  parolfactory  area  (of  Broca).  Its  fibers  rise  in 
the  olfactory  triangle;  they  ascend  through  the  gyrus  subcallosus 
to  the  corpus  callosum,  around  which  they  describe  almost  a 
complete  circuit  through  the  gyrus  supracallosus  (medial 
longitudinal  stria),  fasciola  cinerea,  and  dentate  fascia  to  the 
hippocampal  formation.     The  intermediate  stria  {stria  olfactoria 


INTERMEDIATE    OLFACTORY    STRIA 


77 


intermedia)  which  is  usually  buried  in  the  triangle  and  per- 
forated substance,  comprises  five  small  strands  of  fibers:  (i) 
The  olfacto-hippocampal  bundle  of  the  fornix.  It  rises  in  the 
olfactory  triangle,  the  anterior  perforated  substance  and  the 


Fig.  32. — Base  of  fore-brain;  gyri  shown  in  outline. 

septum  pellucidum,  and  ends  in  the  hippocampus.  (2).  The 
olfacto-amygdalate  bundle  has  the  same  origin;  it  crosses  almost 
completely  through  the  anterior  commissure  and  runs  as  stria 
terminalis  to  the  nucleus  amygdalae;  a  few  of  its  fibers  end  in 


78  THE    CEREBRUM 

the  thalamus  on  the  side  of  its  origin.  (3)  The  olf  acto-habenular 
bundle  rises  in  the  anterior  perforated  substance  and  septum 
pellucidum;  it  ascends  to  the  thalamus  and  runs  through  the 
stria  thalami  to  the  nucleus  habenulae,  chiefly  the  opposite  one. 
(4)  The  olfacto-mesencephalic  bundle  (basal  bundle  of  Wallen- 
berg) rises  in  the  cortex  of  the  olfactory  tract;  descending  as 
far  as  the  spinal  cord,  it  gives  off  fibers  to  tuber  cinereum,  cor- 
pus mammillare,  tegmentum  of  mid-brain,  pons,  etc.  (5)  The 
commissural  olfactory  bundle,  which  extends  from  the  cor- 
tex of  the  olfactory  tract,  through  the  anterior  commissure 
and  through  the  olfactory  tract  of  the  opposite  side  to  the 
granular  and  glomerular  layers  of  the  olfactory  bulb. 

The  Olfactory  Triangle  and  the  Parolfactory  Area  {of  Br  oca). — 
The  triangular  portion  of  the  cortex  between  the  medial  and 
lateral  olfactory  striae,  called  the  triangle  {trigonum  olfactorium) 
is  continuous  medially  with  the  area  par  olf  actor  ia.  The  medial 
stria  marks  the  boundary  between  them  (Figs.  31  and  33). 
Both  are  bounded  behind  by  the  sulcus  par  olf  actor  ius  posterior 
(transverse  part),  and  the  obhque  part  of  the  same  sulcus 
separates  the  parolfactory  area  from  the  gyrus  subcallosus 
(peduncle  of  the  corpus  callosum).  The  olfactory  triangle  is 
a  wedge-shaped  mass  of  gray  substance  (olfactory  tubercle) 
at  the  caudal  end  of  the  olfactory  tract.  It  is  prolonged  for- 
ward in  the  olfactory  sulcus,  as  the  dorsal  border  of  the  olfactory 
tract;  that  prolongation  constitutes  the  cortex  of  the  tract. 
The  olfactory  triangle  is  retrogressive  in  the  adult  brain. 
At  the  fifth  month  in  utero  it  is  more  prominent;  it  is  divided 
into  two  definite  parts,  viz.,  the  gyrus  olfactorius  medialis, 
persisting  as  parolfactory  area,  and  the  gyrus  olfactorius 
lateralis,  which  trends  lateralward  to  the  threshold  of  the  island ; 
there,  it  forms  a  sharp  angle  and,  proceeding  medianward, 
ends  at  the  uncus  hippocampi.  A  small  branch  of  the  lateral 
olfactory  gyrus  disappears  on  the  orbital  surface  of  the  frontal 
lobe.  The  medial  and  lateral  olfactory  gyri  are  faintly  indi- 
cated on  the  adult  brain  by  the  medial  and  lateral  striae. 
The  area  parolfactoria  (Brocae)  is  Hmited  in  front  by  a  slight 
curved    depression,     the    sulcus    par  olf  actor  ius  anterior.     On 


TENTORIAL   AREA  79 

the  medial  surface  it  ascends  between  the  anterior  and  posterior 
parolfactory  sulci  to  the  corpus  callosum  and  becomes  con- 
tinuous with  the  lateral  part  of  the  gyrus  supracallosus. 

The  anterior  perforated  substance  {substantia  perforata  anterior) 
of  the  pars  posterior  rhinencephali  requires  further  mention 
(Fig.  31).  It  is  separated  from  the  triangle  by  a  very  faint 
groove,  the  posterior  sulcus  parolfactorius.  Medially,  it  is  in 
direct  continuity  with  the  tuber  cinereum.  The  optic  tract 
bounds  it,  postero-medially.  Laterally,  it  forms  the  limen 
insulce  in  the  floor  of  the  fossa  cerebri  lateralis,  where  it  is 
overlapped  by  the  temporal  lobe.  Superiorly,  it  is  continuous 
with  the  base  of  the  corpus  striatum.  Coursing  along  the 
inner  and  outer  borders  of  the  anterior  perforated  substance  are, 
respectively,  the  gyrus  diagonalis  and  lateral  olfactory  stria, 
which  converge  and  meet  in  the  hippocampal  gyrus.  The 
perforations  of  this  area  are  for  the  antero-lateral  ganglionic 
arteries. 

The  olfactory  triangle,  the  cortex  of  the  tract,  the  parol- 
factory area  and  the  anterior  perforated  substance,  together 
with  the  septum  pellucidum,  constitute  a  complete  relay  in 
the  olfactory  path;  they  contain  the  bodies  of  the  third  order 
neurones. 

Tentorial  Area  of  the  Basal  Surface  (Figs.  31,  28  and  34). — 
From  the  temporal  pole  backward,  the  basal  surface  of  the 
cerebral  hemisphere  presents  three  nearly  parallel  gyri,  viz., 
the  first  includes  the  inferior  temporal  and  lateral  occipital 
gyri  J  which  form  the  infero-lateral  border;  the  fusiform  gyrus  is 
the  middle  one;  and,  third,  the  gyrus  lingualis  and  the  gyrus 
hippocampi,  which  Hes  next  the  mid-brain.  The  last  belongs 
to  the  gyrus  fornicatus  of  the  Umbic  lobe;  it  is  continuous, 
posteriorly,  with  the  lingual  gyrus,  which  forms  a  part  of  the 
medial  occipital  border  of  the  cerebral  heimsphere.  The  fusi- 
form and  inferior  temporal  gyri  belong  to  the  inferior  surface 
of  the  temporal  and  occipital  lobes.  These  two  lobes  are 
directly  continuous  with  each  other  on  their  inferior  surfaces, 
and  are  only  separated  arbitrarily  by  an  imaginary  line  drawn 
from  the  preoccipital  notch  to  the  anterior  end  of  the  calcarine 


8o  THE   CEREBRUM 

fissure.  They  are  only  partially  separated  from  the  gyrus 
hippocampi;  the  ectorhinal  sulcus  {s.  rhinalis)  and  the  anterior 
part  of  the  collateral  fissure  lie  between  the  temporal  lobe  and 
the  hippocampal  gyrus  of  the  limbic  lobe;  while  the  inferior 
surface  of  the  occipital  lobe  is  continuous  with  the  gyrus  hip- 
pocampi but  is  separated  from  the  gyrus  cinguli,  of  the  limbic 
lobe,  by  the  anterior  calcarine  fissure.  The  fissures  and  sulci 
of  the  tentorial  area  are  the  following: 

Chorioidal  fissure  (f.  chorioidea) 
Hippocampal  fissure  (f.  hippocampi) 
Ectorhinal  sulcus  (s.  ectorhinalis) 
Collateral  fissure  (f.  collateralis) 
Inferior  temporal  sulcus  (s.  temporalis  inferior) 
Calcarine  fissure  (f .  calcarina)  end  of  it. 

The  chorioidal  fissure  (/".  chorioidea)  forms  a  part  of  the 
medial  boundary  of  the  tentorial  area  (Figs.  31  and  34). 
At  the  surface  it  appears  to  be  identical  with  the  hippocampal 
fissure;  but,  upon  looking  deeper,  the  two  are  found  to  be 
separated  by  the  fascia  dentata  and  the  crus  of  the  fornix.  This 
fissure  is  separated  from  the  inferior  horn  of  the  lateral  ventricle, 
only  by  a  layer  of  epithelium,  derived  from  the  roof  plate  of 
the  telencephalon.  It  contains  the  chorioid  plexus  of  the 
inferior  horn. 

Hippocampal  Fissure  (F.  hippocampi,  Fig.  34).^ — Between 
the  mid-brain  and  concave  border  of  the  hippocampal  gyrus 
is  the  crescentic .  fissure  known  as  the  hippocampal  fissure. 
The  fissure  in  front  is  closed  by  the  uncus.  It  extends  backward 
to  the  splenium  of  the  corpus  callosum  where,  in  the  adult,  it 
is  continuous  with  the  furrow  behind  and  above  the  corpus 
callosum,  called  the  callosal  sulcus.  The  hippocampal  is  a 
true  fissure  as  it  is  a  cleft  between  the  mesencephalon  and  the 
telencephalon.  In  its  floor  lie  the  fascia  dentata  and  the  fimbria 
hippocampi  (crus  fornicis);  anterior  to  these  structures  it  is 
continuous  with  the  chorioidal  fissure.  Though  the  hippo- 
campal fissure  is  parallel  with  it,  it  does  not  produce  the  hippo- 
campus seen  in  the  inferior  horn  of  the  lateral  ventricle  (see 
medial  surface  of  the  cerebral  hemisphere). 


SULCI  AND   FISSURES  8 1 

Ectorhinal  Sulcus  (Incisura  temporalis,  Figs.  31  and  35). — 
Midway  between  the  temporal  pole  and  the  hook-point  of  the 
hippocampal  gyrus  is  a  slight  notch,  called  the  ectorhinal  sulcus, 
which  represents  an  iniportant  lateral  boundary  of  the  rhinen- 
cephalon  in  animals  with  highly  developed  sense  of  smell.  It 
indicates  in  man  the  boundary  between  the  hippocampal  and 
fusiform  gyri.  A  half  inch  behind  the  ectorhinal  sulcus  is  the 
anterior  end  of  the  collateral  fissure. 

Fissura  Collateralis  (Figs.  31  and  34). — The  collateral  fissure 
extends  in  a  somewhat  curved  course  from  near  the  temporal 
pole  almost  to  the  occipital  pole.  Its  anterior  two-thirds 
separates  the  hippocampal  from  the  fusiform  gyrus;  its  pos- 
terior one-third  completes  the  medial  and  upper  boundary  of 
the  fusiform  gyrus  and  separates  it  from  the  gyrus  lingualis. 

Inferior  Temporal  Sulcus  (Fig.  31). — Only  one  sulcus  belongs 
wholly  within  the  inferior  surface  of  the  temporal  and  occipital 
lobes.  It  extends  from  a  point  near  the  occipital  pole  forward 
along  the  infero-lateral  border  of  the  hemisphere  almost  to  the 
temporal  pole,  and  incompletely  separates  the  inferior  temporal 
gyrus  and  the  lateral  occipital  gyrus  from  the  gyrus  fusiformis. 
Very  frequently  the  sulcus  has  two  or  more  interruptions.  It 
may  be  called  the  occipito-temporal  sulcus. 

Gyrus  Fusiformis. — One  gyrus  only  is  found  entirely  within 
the  inferior  temporo-occipital  region  (Figs.  31  and  35).  That 
is  the  fusiform  (occipito-temporal  gyrus).  It  extends  from 
near  the  occipital  pole  forward  and  forms  the  temporal  pole. 
The  posterior  nine-tenths  of  its  medial  boundary  is  formed  by 
the  collateral  fissure  and  the  anterior  one-tenth  by  an  imaginary 
line  and  the  ectorhinal  sulcus;  laterally,  it  is  bounded  by  the 
inferior  temporal  sulcus. 

Gyrus  Lingualis.- — The  gyrus  Hngualis  lies  above  and  medial 
to  the  posterior  one-third  of  the  collateral  fissure;  inferior  and 
lateral  from  the  calcarine  fissure.  It  is  continuous  with  the 
gyrus  hippocampi  of  the  limbic  lobe  in  front.  The  gyrus 
lingualis  (Fig.  29)  forms  nearly  all  of  the  medial  occipital 
border  of  the  hemisphere.  It  contains  a  part  of  the  receptive 
visual  center  (Figs.  75  and  77). 
6 


S2  THE    CEREBRUM 

Limbic  Lobe  (Lobus  Limbus),  Liferior  Part. — The  gyrus 
hippocampi  of  this  lobe  is  visible  on  the  inferior  surface  of  the 
fore-brain  (Fig.  3 1) .  Notice  how  this  crescentic  gyrus  embraces 
in  its  concavity  the  section  of  the  mid-brain.  It  is  separated 
from  the  fusiform  gyrus  by  the  collateral  fissure  and  the 
ectorhinal  sulcus;  and  bounded  medially  by  the  hippocampal 
fissure.  The  anterior  end  of  the  gyrus  is  flexed  inward  and 
backward  over  the  end  of  the  hippocampal  fissure  and  the 
whole  anterior  part  constitutes  the  imcus  hippocam.pi.  The 
region  of  the  uncus  is  somewhat  irregular  and,  in  a  four-month 
embryo,  presents  the  gyrus  circumambiens  and  the  gyrus 
semilunaris  described  by  Retzius.  It  represents  the  greater 
part  of  the  lobus  pyraformis  of  osmatic  mammals  and  is 
probably  the  chief  receptive  center  of  smell;  it  receives  the 
lateral  stria  of  the  olfactory  tract  and  fuses  with  a  low  oblique 
ridge,  the  gyrus  diagonalis  of  Broca,  which  in  front  is  continuous 
with  the  gyrus  subcallosus  (or  peduncle  of  the  corpus  callosum) . 

If  the  hippocampal  gyrus  be  drawn  downward  somewhat,  a 
rudimentary  gyrus  may  be  seen  in  the  floor  of  the  hippocampal 
fissure,  between  the  gyrus  hippocampi  and  the  fimbria.  That 
gyrus  is  the  fascia  dentata.  The  fascia  dentata  is  continuous 
posteriorly  with  two  small  gyri,  the  fasciola  cinerea  and  gyrus 
subsplenialis,  both  under  the  splenium  of  the  corpus  callosum, 
by  means  of  which  it  is  linked  to  the  gyrus  supracallosus;  ante- 
riorly the  fascia  dentata  sinks  into  the  concavity  of  the  uncus 
and  bends  at  a  right  angle,  the  angulus  fascice  dentatce,  then  it 
winds  medially  and  upward  over  the  free  end  of  the  uncus,  as  the 
pars  transversa  of  the  dentate  fascia  (band  of  Giacomini) ;  it  fades 
away  on  the  superior  surface  of  the  uncus.  The  pars  transversa 
of  the  fascia  dentata  marks  the  boundary  line  between  the 
gyrus  intralimhicus  behind  it  and  the  nucleus  amygdalce,  which 
is  in  front  of  it. 

Having  studied  the  basal  structures  of  the  cerebral  hemi- 
spheres, it  is  now  in  order  to  examine  the  median  structures  in 
the  inferior  surface  of  the  fore-brain.  They  occupy  the  inter- 
peduncular or  hypophyseal  region.  They  constitute  the 
hypothalamus  and  form  part  of  the  floor  of  the  third  ventricle. 


HYPOTHALAMUS  83 

The  hypothalamus  is  the  name  applied  to  the  cerebral  struc- 
tures under  the  thalamus.  Posteriorly  it  blends  with  the  mid- 
brain. Its  free  portion  is  divided  into  two  parts,  viz.,  the  pars 
Optica  hypothalami  and  the  pars  mammillaris  hypothalami. 
The  former  belongs  to  the  telencephalon,  the  latter  to  the 
diencephalon.     They  include  the  following: 


Pars  Optica  Hjrpothalami  < 


Lamina  cinerea  terminalis. 
Optic  chiasma  (chiasma  opticum) 
Tuber  cinereum 

Infundibulum  and 

Hypophysis. 


Pars  Mammillaris  Hypothalami  {  Corpora  mammillaria. 

The  lamina  cinerea  terminalis  (Fig.  33)  is  the  most  superior  of 
the  median  structures.  It  is  a  thin  lamina  of  ash-colored 
(cinereum)  gray  matter  closing  the  end  of  the  neural  tube.  It 
extends  from  the  anterior  superior  surface  of  the  optic  chiasma 
upward  and  backward  to  the  anterior  commissure,  just  in  front 
of  which  it  becomes  continuous  with  the  lamina  rostralis  of  the 
corpus  callosum.  Laterally,  it  is  continuous  with  the  cortex 
of  the  cerebral  hemisphere.  Behind  it  is  the  third  ventricle; 
in  front  of  it,  a  part  of  the  longitudinal  fissure  of  the  cerebrum. 

Optic  Chiasma  {Chiasma  opticum). — The  optic  chiasma  is 
a  quadrilateral  sheet  of  nerve  fibers  whose  anterior  angles 
receive  the  optic  nerves  and  whose  posterior  angles  give  off  the 
optic  tracts  (Fig.  21) .  With  the  nerves  and  tracts  attached,  it  is 
x-shaped.  The  chiasma  is  a  median  structure  and  is  situated 
beneath  the  lamina  cinerea,  in  the  optic  groove  of  the  sphenoid 
bone.  The  fibers  of  the  optic  nerves  and  tracts  compose  it. 
There  are  three  sets  of  these  fibers,  namely,  the  inter  cerebral, 
the  direct,  and  the  decussating.  A  fourth  group  of  fibers,  called 
the  interretinal  and  said  to  be  commissural  for  the  retinae, 
has  been  hitherto  described,  but  their  existence  is  very  doubtful. 
The  intercerebral  fibers  are  not  found  in  the  optic  nerves,  but 
form  the  inferior  commissure  (Guddeni)  which  joins  together 
the  medial  geniculate  bodies  (Fig.  5  5) .  The  direct  (or  temporal) 
and  decussating  (or  nasal)  fibers  run  through  nerve  and  tract 


84  THE   CEREBRUM 

and  join  the  retina  with  the  brain  on  the  same  and  the  opposite 
sides,  respectively.  In  most  vertebrates  below  mammals,  and 
in  the  mouse  and  guinea-pig,  it  is  said  that  the  optic  fibers  all 
decussate  in  the  chiasma.  Normally  in  man  and  the  highei 
mammals,  the  temporal  half  of  each  retina  contributes  to  the 
tract  direct  fibers  and  the  nasal  half  crossed  fibers  (Fig.  67). 
The  optic  nerves  {nervi  optici)  extend  from  the  foramen  sclerae 
of  each  eyeball  back  to  the  front  of  the  chiasma,  through  the 
optic  foramina;  they  rise  in  the  ganglionar  cells  of  the  retinae, 
which  are  connected  with  the  rods  and  cones  by  the  bipolar 
neurones.  The  optic  tracts  {tractus  optici)  connect  the  chiasma 
with  the  brain.  Each  tract  winds  outward  and  backward 
around  the  cerebral  peduncle,  and  divides  into  a  medial  and  a 
lateral  root  (Fig.  55).  The  roots  wind  under  the  thalamus  and 
disappear  at  the  corresponding  geniculate  body.  The  lateral 
root  contains  all  the  retinal  fibers,  the  medial  root  has  nothing 
to  do  with  vision.  The  fibers  of  the  lateral  root  {radix  lateralis) 
may  be  traced  to  the  lateral  geniculate  body  (80  per  cent.  Von 
Monokow),  to  the  pulvinar  of  the  thalamus  (nearly  all  the  20 
per  cent,  remaining),  and  the  rest  to  the  superior  quadrigeminal 
colHculus.  The  optic  radiation  of  the  capsule  connects  these 
centers  with  the  medial  occipital  cortex.  Like  other  sensory 
nerves,  the  optic  sends  a  few  fibers  to  the  cerebellum,  which 
are  concerned  with  coordinated  movements.  The  medial  root 
rises  and  ends  in  the  medial  geniculate  body  and  thalamus.  Its 
fibers  form  the  commissura  inferior  (Guddeni). 

Tuber  Cinereum. — The  posterior  border  of  the  optic  chiasma 
is  contiguous  to  the  tuber  cinereum  (Figs.  21  and  31).  Here 
the  gray  matter  is  thickened  and  centrally  prominent.  The 
bulbous  infundibulum  projects  downward  from  it  to  rest  in  the 
sella  turcica,  where  it  forms  the  posterior  lobe  of  the  hypophysis. 
The  upper  end  of  the  infundibulum  is  hollow  (f unnel-Hke) .  Its 
cavity  forms  the  lowest  part  of  the  third  ventricle.  In  man  the 
bulb  of  the  infundibulum  is  solid  at  maturity,  though  hollow  in 
the  embryo.  It  is  composed  largely  of  fibrous  tissue,  notwith- 
standing the  fact  that  it  is  developed  from  the  floor  of  the  telen- 
cephalon.    From  the  base  (superior  end)  of  the  infundibulum, 


HYPOPHYSIS 

the  tuber  cinereum  extends  in  continuity  with  the  anterior  per- 
forated substance  on  each  side  of  it;  and  behind  the  corpora 
mammillaria  mark  the  boundary  between  it  and  the  posterior 
perforated  substance  of  the  mid-brain.  In  its  antero-lateral 
part,  near  the  optic  tract,  the  tuber  cinereum  contains  the 
supra-optic  nucleus  of  Cajal,  comprising  an  anterior,  a  posterior 
and  a  dorsal  group  of  cells,  which  some  consider  to  be  the  source 
of  the  intercerebral  fibers  of  the  optic  chiasma.  The  tuber 
cinereum  sometimes  presents  a  second  projection,  behind  the 
infundibulum,  called  the  eminentia  saccularis;  this  is  believed 
to  represent  the  saccus  vasculosis  of  fishes. 

The  lamina  cinerea  and  tuber  cinereum  form  the  inferior  gray 
commissure  of  the  fore-brain. 

The  hypophysis  (pituitary  body,  Fig.  21)  is  composed  of  two 
lobes  bound  together  by  connective  tissue.  A  sheet  of  dura 
mater  (diaphragma  sellce)  holds  them  in  the  hypophyseal  fossa. 
The  anterior  lobe,  the  larger,  is  derived  from  the  epithelium  of  the 
mouth  cavity;  and,  in  structure,  resembles  the  thyreoid  gland. 
Its  closed  vesicles,  lined  with  columnar  epithelium  (in  part 
ciliated),  contain  a  viscid  jelly-Hke  material  (pituita),  which 
suggested  the  old  name  for  the  body.  The  anterior  lobe  is 
hollowed  out  on  its  posterior  surface  (kidney-shape)  and  receives 
the  posterior  lobe,  the  infundibulum,  into  the  concavity.  The 
hypophysis  has  an  internal  secretion  which  appears  to  stimulate 
the  growth  of  connective  tissues  and  to  be  essential  to  sexual 
development.  The  active  hormone  is  found  in  the  posterior 
lobe,  the  pars  nervosa;  the  anterior  lobe  contains  only  a  colloid, 
eosinophile  material.  According  to  Harvey  Gushing,  an  excess 
of  this  hormone,  in  youth,  causes  giantism ;  in  the  adult  it  produces 
acromegaly.  While,  on  the  other  hand,  deficiency  in  childhood 
is  associated  with  small  stature,  excessive  fat  and  eunuchism; 
and,  if  the  deficiency  develop  in  the  grown-up,  there  is  sexual 
atrophy  and  disappearance  of  the  signs  of  adolescence. 

Corpora  Mammillaria  (Figs.  21  and  31).— Two  white  bodies 
(corpora  albicantia),  as  large  as  a  small  pea,  are  situated  one  on 
either  side  of  the  median  line,  between  the  tuber  cinereum  and 
the  pigmented  gray  matter  of  the  posterior  perforated  substance. 


86  THE   CEIIEBRUM 

Being  produced  by  the  division  of  a  single,  median  body  in  the 
embryo,  they  remain  in  the  adult  in  close  apposition.  Each 
is  formed  superficially  by  a  loop  in  the  columna  of  the  fornix 
and  is,  therefore,  composed  of  white  substance  at  the  surface. 
There  is  gray  matter  in  the  interior  which  forms  a  round  medial 
and  a  crescentic  lateral  nucleus  (Fig.  58).  In  the  medial 
nucleus  the  fornix  fibers  terminate  and  an  ascending  bundle 
rises,  called  the  fasciculus  mammillaris  princeps;  this  bundle 
divides  Y-like  into  mammillo4halamic  (or  thalamo-mammillary) 
bundle,  which  ends  in  the  thalamus,  and  mammillo-tegmental 
(or  tegmento-mammillary)  bundle,  which  descends  to  the  teg- 
mentum of  the  mid-brain,  pons,  etc.  The  lateral  nucleus  of 
the  mammillary  body  gives  rise  to  a  small  fasciculus  which 
terminates  in  the  tegmentum  of  the  mid-brain;  it  is  called  the 
peduncle  of  the  mammillary  body. 

Immediately  behind  the  corpora  mammillaria  is  the  posterior 
perforated  substance  (Figs.  21  and  31).  This  is  the  exposed 
part  of  the  substantia  nigra  of  the  mid-brain,  perforated  for  the 
passage  of  the  postero-median  ganghonic  arteries.  The  pons 
and  bases  pedunculi  bound  it  behind.  Issuing  from  the  inner 
side  of  the  basis  pedunculi  is  the  large  oculomotor  nerve;  and 
coursing  over  its  surface  from  behind  forward,  is  the  smaller 
trochlear  nerve.  The  bases  pedunculi  will  be  described  with 
the  mid-brain  to  which  they  belong. 

FISSURES  OF  THE  MEDIAL  AND  TENTORIAL  SURFACE 

To  expose  the  medial  surface  of  the  cerebral  hemispheres,  a 
median  sagittal  section  must  be  made  through  the  connecting 
links  of  the  hemispheres  and  the  inter-brain,  dividing  the  fore- 
brain  into  lateral  halves.  Separate  the  lips  of  the  longitudinal 
fissure  of  the  cerebrum;  drop  the  moistened  brain-knife  down 
onto  the  corpus  callosum;  and  make  one  quick  sweep  of  the 
knife  toward  you.  Of  the  surface  now  exposed  the  middle  one- 
third  is  produced  by  section. 

It  is  convenient  to  study  the  tentorial  area  of  the  basal  surface 
with  the  medial  surface  (Fig.  31).  In  this  medial  and  tentorial 
surface  there  are  eight  important  sulci  and  four  fissures  (Fig.  34). 


Sulci 


Fissures 


CINGULATE   SULCUS  87 

Of  cingulum  (s.  cinguli) 

Callosal  (s.  corporis  callosi) 

Subparietal  (s.  subparietalis) 

Occipito-parietal  (s.  occipito-parietalis) 

Inferior  temporal  (s.  temporalis  inferior) 

Ectorhinal  (s.  ectorhinalis) 

Parolfactory  (ss.  parolfactorius  ant.  and  post). 

Calcarine  (fissura  calcarina) 
Hippocampal  (f.  hippocampi) 
Chorioidal  (f.  chorioidea) 
.  Collateral  (f.  collateralis). 


Sulcus  Cinguli  (Calloso-marginal  Sulcus). — Beginning  under 
the  middle  cut  surface  and  extending  in  a  curve  forward,  up- 
ward, and  backward,  until  it  half  encircles  the  corpus  callosum; 
and  then  turning  upward  to  the  supero-medial  border  and 
ending  just  behind  the  central  sulcus  is  the  sulcus  cinguli  (Figs. 
33  and  34).  It  separates  the  gyrus  cinguli  and  a  marginal 
gyrus,  including  the  straight  and  superior  frontal,  from  one 
another  by  its  anterior  part;  and  by  its  marginal  end  separates 
the  paracentral  lobule  from  the  praecuneus.  The  sulcus  cinguli 
is  usually  interrupted  by  one  annectant  gyrus  and  often  by 
two.  These  indicate  its  development  in  three  separate  parts. 
Several  branches  radiate  from  the  cingulate  sulcus  toward  the 
supero-medial  border  of  the  hemisphere;  the  most  constant 
is  the  sulcus  paracentralis,  which  rises  a  short  distance  in 
front  of  the  marginal  part  and  forms  the  anterior  boundary  of 
the  paracentral  lobule. 

At  its  beginning  under  the  corpus  callosum,  the  sulcus  cinguli 
is  almost  continuous  with  a  small  curved  sulcus,  which  runs 
nearly  vertically  downward,  called  the  anterior  parolfactory 
sulcus  (Figs.  34  and  35).  Behind  that  little  sulcus  there  is  a 
small  curved  gyrus,  the  parolfactory  area  (of  Broca),  which  is 
continuous  with  the  lateral  stria  of  the  gyrus  supracallosus; 
the  parolfactory  area  is  bounded  behind  by  another  slight 
sulcus,  called  the  posterior  parolfactory  sulcus.  The  latter 
separates  the  area  parolfactoria  from  the  gyrus  subcallosus. 

Subparietal  Sulcus. — About  one  inch  above  and  behind  the 
posterior  end  of  the  corpus  callosum  there  is  an  irregular  sulcus, 


ss 


THE   CEREBRUM 


called  the  subparietal,  which  separates  the  gyrus  cinguli  of  the 
limbic  lobe  from  the  praecuneus  of  the  parietal  lobe  (Fig.  34). 
Sometimes  it  is  continuous  with  the  cingulate  sulcus,  at  the 


junction  of  the  marginal  part;  in  most  brains  it  is  an  independent 
sulcus  having  the  shape  of  a  very  broad  X. 

The  callosal  sulcus  is  the  deep  furrow  between  the  corpus 
callosum  and  the  gyrus  cinguli.     It  follows  the  convexity  of  the 


LAMBDA-SHAPED    SULCUS  89 

corpus  callosum  and  was  formerly  called  the  ventricle  of  it  (Fig. 
34).  The  callosal  sulcus,  behind  the  corpus  callosum,  is  con- 
tinuous with  the  hippocampal  fissure. 

The  occipito-parietal  sulcus  (Figs.  20,  33  and  34),  the  inter- 
nal part,  extends  downward  from  the  supero-medial  border  to 
the  middle  of  the  calcarine  fissure.  The  two  form  a  lambda- 
shaped  fissure  ^  (Fig.  34) ;  the  lambda  being  tilted  toward  the 
frontal  pole  has  one  anterior  and  two  posterior  rami.  The 
anterior  ramus  and  the  lower  of  the  posterior  rami  constitute 
the  calcarine  fissure;  the  posterior  superior  ramus  is  the 
occipito-parietal  sulcus.  This  latter  sulcus  cuts  the  supero- 
medial  border  at  the  junction  of  the  posterior  one-sixth  with  the 
anterior  five-sixths  of  that  border;  it  is  situated  about  two 
inches  above  the  occipital  pole,  and  lies  one-sixth  of  an  inch 
anterior  to  the  point  in  the  skull  called  the  lambda.  It  sepa- 
rates the  parietal  lobe  from  the  cuneus  of  the  occipital  lobe. 
The  occipito-parietal  sulcus  is  a  deep  one.  In  the  embryo  the 
primary  occipito-parietal  fissure  produces  an  eminence  in  the 
posterior  horn  of  the  lateral  ventricle  (Cunningham).  It  is 
then  a  true  fissure.  But  that  primitive  fissure  and  the  ventricu- 
lar eminence  entirely  disappear,  and  the  adult  sulcus  is  a 
secondary  and  superficial  furrow,  hence  it  is  properly  called  a 
sulcus  and  not  a  fissure.  At  the  inferior  end  of  the  occipito- 
parietal sulcus  a  buried  annectant  gyrus,  the  gyrus  cunei, 
separates  the  occipito-parietal  sulcus  from  the  calcarine 
fissure,  with  which  superficially  it  is  continuous. 

The  calcarine  fissure  begins  a  quarter  of  an  inch  below  the 
posterior  end  of  the  corpus  callosum  and  runs  backward  and 
slightly  upward  to  the  lower  end  of  the  occipito-parietal  sulcus ; 
and  then  curves  downward  to  a  point  near  the  occipital  pole 
where  it  ends  bifid  (Figs.  31  and  34).  It  is  thus  divided  by  the 
sulcus  occipito-parietalis  into  an  anterior  calcarine  and  a  pos- 
terior calcarine  fissure.  These  three  furrows  are  continuous  with 
one  another  superficially  in  the  human  brain;  but  buried  annec- 
tant gyri  actually  separate  them  from  each  other:  the  gyrus 
cunei  separates  the  occipito-parietal  sulcus  from  the  calcarine 
fissure  and  the  anterior  calcarine  fissure  is  separated  from  the 


90 


THE    CEREBRUM 


HIPPOCAMPAL   AND   CHORIOIDAL   FISSURES  9I 

posterior  calcarine  by  the  gyrus  cuneo-lingualis  (Cunningham.) 
The  anterior  calcarine  fissure  indents  the  medial  wall  of  the 
posterior  horn  of  the  lateral  ventricle,  producing  the  calcar  avis. 

Hippocampal  Fissure  (Figs.  32  and  34). — ^A  crescentic  fissure, 
convex  downward,  begins  under  the  splenium  of  the  corpus 
callosum  in  continuity  with  the  callosal  sulcus  and  winds 
forward  beneath  the  thalamus  to  within  an  inch  of  the  temporal 
pole  where  it  is  closed  by  the  uncus.  It  is  the  hippocampal 
fissure,  an  embryonic  cleft  between  the  hemisphere  vesicle  and 
the  mesencephalon.  In  the  floor  of  this  fissure  lie  the  dentate 
fascia,  and  the  fimbria  hippocampi  and  crus  fornicis.  Anterior 
to  the  crus  and  fimbria  there  is  a  deep  crescentic  cleft  in  the 
hemisphere,  called  the  chorioidal  fissure;  behind  them  runs  the 
fimhriodentate  sulcus  between  the  fimbria  and  the  fascia  dentata. 
The  fascia  dentata  is  separated  from  the  hippocampal  gyrus 
by  a  very  superficial  groove,  the  sulcus  hippocampi  (formerly 
called  the  hippocampal  fissure),  which  is  parallel  with  the 
ventricular  eminence,  called  the  hippocampus,  but  does  not 
produce  it.  Elliot  Smith  has  shown  that  the  hippocampus  is 
not  an  indentation  of  the  hemisphere  but  a  thickening  of  it. 

The  hippocampal  fissure  contains  a  considerable  extension 
of  the  subarachnoid  space.  As  it  winds  around  the  mid-brain 
it  is  named  the  cisterna  amhiens  mesencephali. 

The  chorioidal  fissure  (Figs.  34  and  45)  describes  about 
two-thirds  of  a  circumference  along  the  concavity  of  the  fornix. 
It  extends  from  near  the  foramen  interventriculare  backward 
over  the  thalamus;  and  then  downward  and  forward  along  the 
floor  of  the  hippocampal  fissure.  The  chorioidal  fissure  is  a 
complete  one,  involving  the  whole  hemisphere  wall.  A  single 
layer  of  epithelium  derived  from  the  roof-plate  separates  it 
from  the  lateral  ventricle.  The  pia  mater,  dipping  into  it, 
forms  the  chorioid  plexus  of  that  ventricle.  The  fissure  is 
peculiar  in  the  fact  that  between  the  inter-brain  and  the  fornix 
there  is  a  transverse  slit  by  means  of  which  it  is  continuous 
with  the  same  fissure  on  the  opposite  side.  In  this  antero- 
superior  part,  which  is  in  direct  continuity  with  the  transverse 


92  THE   CEREBRUM 

fissure  of  the  cerebrum,  is  the  border  of  the  chorioid  tela  of  the 
third  ventricle. 

Collateral  Fissure. — The  collateral  is  a  long  fissure  (Figs. 
31  and  34).  It  reaches  from  near  the  occipital  almost  to  the 
temporal  pole.  It  is  situated  below  and  parallel  with  the  cal- 
carine  and  hippocampal  fissures,  being  separated  from  the 
former  by  the  lingual  gyrus  and  from  the  latter  by  the  hippo- 
campal gyrus.  The  gyrus  fusiformis  lies  below  and  lateral  to 
this  fissure.  Anterior  to  the  collateral  fissure,  there  is  a  small 
sulcus  between  the  gyrus  hippocampi  and  the  temporal  pole, 
called  the  ectorhinal  stilcus,  which  represents  a  very  important 
fissure  (/.  rhinalis)  in  osmatic  animals.  The  collateral  fissure 
is  occasionally  interrupted  by  two  annectant  gyri  and  divided 
into  a  temporal,  an  occipital  and  an  intermediate  part.  This 
signifies  a  persistence  of  its  embryonic  condition.  The  inter- 
mediate portion,  sometimes  assisted  by  the  anterior  part, 
indents  the  ventricular  wall  and  produces  the  eminentia  col- 
lateralis  in  the  inferior  horn  of  the  lateral  ventricle. 

The  inferior  temporal  sulcus  is  usually  a  series  of  indenta- 
tions rather  than  a  continuous  sulcus  (Figs.  31  and  34).  It  is 
about  equal  in  extent  to  the  collateral  fissure  from  which  it  is 
separated  by  the  fusiform  gyrus.  It  is  parallel  with  the  infero- 
lateral  border  of  the  cerebral  hemisphere.  As  the  inferior  tem- 
poral gyrus,  which  forms  this  border  reaches  over  onto  the 
tentorial  area  a  variable  distance,  even  in  the  two  sides  of  the 
same  brain,  the  position  of  the  inferior  temporal  sulcus  is  not 
c(5nstant;  but  it  is  usually  one-quarter  or  one-half  inch  medial 
to  the  border. 

LOBES  AND  GYRI    OF  MEDIAL  AND  TENTORIAL  SURFACE 

The  gyri  form  two  concentric  rings,  interrupted  antero- 
inferiorly  at  the  fossa  cerebri  lateralis,  which  encircle  the  corpus 
callosum  and  thalamus  (Fig.  34).  The  two  rings  are  separated 
from  one  another  by  a  broken  fissure,  the  limbic  fissure,  made 
up  of  the  sulcus  cinguli  (except  its  marginal  end),  the  subparietal 
sulcus,  the  anterior  part  of  the  calcarine  and  of  the  collateral 
fissures  and  the  ectorhinal  sulcus. 


GYRUS   FORNICATUS  93 

Gyrus  Fomicatus. — The  gyrus  cinguli  and  the  gyrus  hippo- 
campi joined  together  at  the  posterior  border  of  the  corpus 
callosum  by  the  isthmus  and  together  constituting  the  gyrus 
fornicatus,  form  the  central  ring.  The  gyrus  cinguli  begins 
anteriorly  under  the  corpus  callosum  in  contiguity  with  the 
area  parolfactoria,  anterior  to  the  fossa  cerebri  lateralis;  and 
the  hippocampal  terminates  as  uncus  just  behind  that  fossa. 
The  gyrus  fornicatus  forms  the  chief  part  of  the  limbic  lobe. 

The  gyrus  cinguli  is  the  arched  gyrus  which  is  inclosed  be- 
tween the  callosal  sulcus  and  the  sulcus  cinguli,  except  above 
the  posterior  end  of  the  corpus  callosum ;  there  it  is  bounded  on 
its  convexity  by  the  subparietal  sulcus  (Fig.  34).  Underneath 
the  frontal  part  of  the  corpus  callosum  in  the  adult  the  end 
of  the  gyrus  cinguli  is  continuous  with  a  small  vertical  gyrus 
called  the  area  parolfactoria  (Brocae),  which  is  embraced  be- 
tween the  anterior  and  posterior  parolfactory  sulci  and  is 
continuous  with  the  area  of  the  same  name  on  the  base  of  the 
cerebral  hemisphere.  This  area  belongs  to  the  cortical  area 
of  smell.  The  posterior  end  of  the  cingulate  gyrus  is  almost 
separated  from  the  hippocampal  gyrus  by  the  anterior  cal- 
carine  fissure;  the  narrow  link  left  between  this  fissure  and  the 
hippocampal  fissure  is  the  isthmus  gyri  fornicati.  It  is  claimed 
by  Schafer  and  others  that  the  superior  part  of  the  gyrus 
cinguli  constitues  a  portion  of  the  somaesthetic  area;  but  the 
histological  investigations  of  Dr.  A.  W.  Campbell  appear  to 
disprove  such  a  claim.  According  to  Paul  Flechsig,  the  gyrus 
cinguli  contains  the  center  of  taste.  He  locates  the  center  in 
the  posterior  part  of  the  gyrus  adjacent  to  the  splenium  of  the 
corpus  callosum;  it  forms  a  thin  zone  bounding  the  callosal 
sulcus  (Fig.  75). 

The  gyrus  hippocampi  (Figs.  31  and  34)  extends  downward 
and  forward,  along  the  hippocampal  fissure,  from  the  isthmus 
to  within  a  half -inch  of  the  temporal  pole.  Its  anterior 
extremity  is  separated  from  the  pole  by  the  ectorhinal  sulcus, 
and  is  bent  upward  and  backward  over  the  end  of  the  hippo- 
campal fissure,  forming  a  sharply  curved  hook,  the  uncus. 
The  hippocampal  gyrus  is  bounded  below  and  laterally  by  the 


94  THE    CEREBRUM 

collateral  fissure.  Posteriorly,  it  is  continuous  with  the  gyrus 
lingualis.  The  reflected  part  of  the  uncus  hippocampi  is 
continuous  with  a  concealed  gyrus,  located  in  the  floor  of  the 
hippocampal  fissure,  viz.,  the  dentate  fascia.  As  already 
described,  the  dentate  fascia  forms  the  transverse  band  cross- 
ing the  medial  side  of  the  reflected  end  of  the  uncus,  called  the 
pars  transversa  fascice  dentatce  (frenulum  of  Giacomini) ;  that 
pars  transversa  separates  the  point  of  the  hook,  the  gyrus 
intralimbicus,  from  the  surface  projection  of  the  nucleus 
amygdalae,  located  in  front  of  that  transverse  band. 

The  fascia  dentata  belongs  to  a  suppressed  gyrus,  very 
retrogressive  in  all  mammals,  which  is  almost  annihilated  by 
the  development  of  the  corpus  callosum.  This  vestige  of  a 
gyrus  extends  from  the  uncus  around  the  corpus  callosum 
from  behind  forward  to  the  parolfactory  area  and  gyrus 
diagonalis.  At  the  posterior  end  of  the  dentate  fascia,  beneath 
the  occipital  end  of  the  corpus  callosum,  the  gyrus  divides  into 
two  parts,  the  fasciola  cinerea  and  the  gyrus  subsplenialis, 
which,  winding  over  the  end  of  the  corpus  callosum,  become 
continuous  with  the  medial  and  lateral  longitudinal  striae 
of  the  gyrus  supracallosus;  inferior  to  the  frontal  end  of  the 
callosum  the  medial  stria  is  continuous  in  turn,  with  the  gyrus 
subcallosus  and  the  gyrus  diagonalis  and  the  lateral  stria  with 
the  parolfactory  area  of  Broca. 

The  uncus  and  the  area  parolfactoria  constitute  the  greater 
part  of  the  receptive  center  of  smell  (Figs.  75  and  77).  In  the 
uncus  anterior  to  the  end  of  the  hippocampal  fissure,  Retzius 
locates  the  gyrus  circumamhiens  and  gyrus  semilunaris,  which 
may  be  identified  in  the  human  embryo;  and  he  declares  them  to 
contain  the  end  of  the  lateral  olfactory  stria  and  of  the  gyrus 
subcallosus,  and  he  thinks  they  form  the  most  important  part 
of  the  receptive  olfactory  center.  This  region  represents  the 
lobus  pyraformis  of  osmatic  animals  and,  according  to  Elliot 
Smith,  it  is  the  only  part  of  the  gyrus  hippocampi  which 
properly  belongs  to  the  rhinencephalon. 

Limbic  Lobe. — The  parts  of  the  limbic  lobe  may  now  be 
enumerated  as  follows:     (i)  The  gyrus  fornicatus  {g.  cinguli 


LIMBIC   LOBE 


95 


and  g.  hippocampi)]     (2)  the  fascia  dentata,  fasciola  cinerea, 
gyrus  subsplenialis,  supracallosal  gyrus  (longitudinal  striae),  and 


^  r!  <-i  fl 


car:  roj^ 


06 


«     «  tj- 
•  S  o 

ao  tfl**^  «-<    . 
**  __ 1^  »-i 

a5    .  ,        2 
'^   S  £  „;  «o  o 

•^   0.0^  ft  00 

rt  «l-  .a 

"C    .0.0*2  3 

I.  s^^^^- 

^  ^    O   ri    n^ 

o  s  c  w  S  g 

^  1>  o 
9I.2S.2 
^-rt-  So 

ai  B.'ce  C.o 
"*  u.S       t- 


subcallosal  gyrus,  gyrus  diagonalis,  and  area  parolfactoria;  (3) 
one-half  of  the  septum  pellucidum;  and  (4)  a  lateral  half  of  the 


96  THE    CEREBRUM 

fornix.  The  limbic  lobe  is  retrogressive  in  the  human  brain. 
The  structures  enumerated  above  under  No.  2  and  No.  3  are 
but  faint  representatives  of  the  strong  dentate  gyrus  seen  in 
animals  having  no  corpus  callosum.  The  development  of  the 
corpus  callosum  encroaches  upon  and  partially  destroys  the 
dentate  gyrus.  The  limbic  lobe  in  part  belongs  to  the  rhinen- 
cephalon.  According  to  the  researches  of  Elliot  Smith  the 
posterior  inferior  part  of  the  gyrus  hippocampi,  that  part 
behind  the  uncus  and  below  the  subiculum  and  the  whole 
gyrus  cinguli  belong  to  the  neopallium  and  not  to  the  rhinen- 
cephalon. 

The  peripheral  ring  on  the  medial  and  tentorial  surface  of  the 
cerebral  hemisphere  is  composed  of  five  gyri,  which  belong  to 
frontal,  parietal,  occipital  and  temporal  lobes  (Figs.  34  and  36). 
Beginning  under  the  corpus  callosum  anterior  to  the  area  parol- 
factoria  and  going  forward  to  the  frontal  pole,  then  along  the 
supero-medial  border  to  the  occipital  pole  and,  finally,  along  the 
iniero-lateral  border  to  the  temporal  pole,  these  gyri  are  as 
follows:  The  gryus  rectus  and  gyrus  frontalis  superior  {g. 
marginalis)  ending  behind  as  lohulus  paracentralis  that  closes 
the  superior  end  of  the  central  sulcus;  these  gyri  are  partially 
subdivided.  The  straight  gyrus  is  divided  by  the  sulcus 
rostralis  and,  sometimes,  by  the  sulcus  subrostralis,  two  cres- 
centic  sulci,  parallel  with  the  first  part  of  the  sulcus  cinguli, 
which  terminate  near  the  supero-medial  border  of  the  hemi- 
sphere in  the  superior  frontal  gyrus.  The  superior  frontal 
gyrus  is  further  divided  by  one  or  more  longitudinal  grooves 
which  may  be  continuous  with  one  another  and  with  the  sulcus 
rostralis;  they  constitute  the  sulcus  paracingularis .  The 
praecuneus  is  inclosed  between  the  marginal  part  of  the  sulcus 
cinguli  and  the  occipito-parietal  sulcus,  and  is  bounded  antero- 
inferiorly  by  the  subparietal  sulcus.  It  belongs  to  the  parietal 
lobe.  The  cuneus  lies  below  the  occipito-parietal  sulcus.  In- 
feriorly  it  is  limited  by  the  posterior  calcarine  fissure,  which 
separates  it  from  the  gyrus  lingualis.  The  cuneus  and  lingual 
gyrus  make  up  the  medial  surface  of  the  occipital  lobe;  the 
lingual  gyrus  forms  the  medial  occipital  border  of  the  cerebral 


VISUAL   CENTER 


97 


hemispheres.  In  the  gyrus  linguali  and  cuneus,  along  the 
calcarine  fissure,  the  receptive  visual  center  is  located.  A  longi- 
tudinal, sulcus  lingualis  sometimes  divides  the  lingual  gyrus 
and  marks  the  lower  limit  of  the  visual  cortex.     The  lingula 


gyrus  is  continuous  with  the  hippocampal  gyrus  in  front;  both 
gyri  are  bounded  below  and  laterally  by  the  collateral  fissure, 
which  intervenes  between  them  and  the  gyrus  fusiformis. 
According  to  Eberstaller,  the  fusiform  gyrus  belongs  wholly 


98 


THE    CEEEBRUM 


to  the  temporal  lobe;  the  collateral  fissure  and  an  inconstant 
branch,  the  transverse  collateral  sulcus  which  ascends  toward 
the  isthmus  of  the  gyrus  fornicatus,  form  the  occipito-temporal 
boundary  in  his  description.  A  very  long  gyrus,  it  extends 
almost  from  the  occipital  to  the  temporal  pole.  It  is  separated 
from  the  inferior  temporal  gyrus  by  an  interrupted  sulcus  near 
the  infero-lateral  border  of  the  hemisphere.  The  inferior 
temporal  gyrus  is  chiefly  on  the  convex  surface. 

The  superior  frontal  gyrus  belongs  to  the  higher  psychic  and 
psychic  motor  region.  The  paracentral  lobule  contains  the 
motor  center  for  the  opposite  foot,  just  in  front  of  the  central 
sulcus;  and  immediately  behind  that  sulcus  is  the  superior  part  of 
the  receptive  somcesthetic  area  (Figs.  7 5  and  77) .  In  the  praecuneus 
is  a  part  of  the  stereo  gnostic  center;  the  remainder  is  in  the 
superior  parietal  lobule;  this  center  belongs  to  the  psychic-sensory 
area.  The  cuneus  and  lingual  gyrus,  along  the  calcarine  fissure 
of  each  hemisphere  constitute  the  receptive  visual  center  for  the 
corresponding  halves  of  both  retinae  and  perhaps  for  both 
maculae  lutese.  It  was  formely  held  that  the  anterior  part  of 
the  fusiform  gyrus,  that  part  just  below  the  uncus,  contains  the 
center  of  taste  (Mills) . 

The  peripheral  ring  of  gyri  seen  on  this  surface  belongs  to 
lobes  which  have  their  largest  exposure  on  the  convex  surface 
of  the  cerebral  hemisphere.  Thus  seven  lobes  belong  to  the 
surface  of  each  hemisphere. 


I.  Seven  lobes 

Frontal 

Parietal 

Temporal 

T.  Neopallium 

Cerebral  Hemisphere 

Occipital 
Island  (of  Reil) 
Limbic                  ^ 

Olfactory,  etc. 

II.  Rhinencephalon  (archipal- 
lium) 

^  2.  Basal  ganglion 

III.  Corpus  striatum. 

VENTRICLES  AND  GROSS  STRUCTURE  OF  THE  FORE-BRAIN 

The  ventricles  of  the  fore-brain  comprise  the  third  ventricle, 
the   aula,    the  interventricular  foramina   and   the   two   lateral 


INTERNAL   CAPSULE  99 

ventricles.  The  third  is  the  ventricle  of  the  inter-brain.  It 
communicates  posteriorly  with  the  fourth  ventricle  through  the 
cerebral  aqueduct;  anteriorly  it  is  in  direct  continuity  with  the 
aula,  which  is  the  median  ventricle  of  the  end-brain.  The  aula 
opens  on  each  side  into  the  ventricle  of  the  cerebral  hemisphere 
through  the  interventricular  foramen  of  Monro.  Being  out- 
side the  median  plane,  the  ventricles  of  the  hemispheres  are  the 
lateral  ventricles.  The  lateral  ventricles,  excepting  the  inferior 
horns,  occupy  a  level  superior  to  the  aula  and  third  ventricle. 
In  a  frontal  section  of  the  fore-brain,  the  ventricles  form  a 
T-like  figure;  the  third  ventricle  and  aula  constitute  the  stem, 
the  two  lateral  ventricles  form  its  branches.  These  ventricles 
are  roofed  over  by  the  white  corpus  calloum,  which  stretches 
from  one  hemisphere  to  the  other;  and  the  converging  internal 
capsules  and  the  basal  ganglia  form  most  of  the  floor  and 
lateral  walls.  The  extent  and  relations  of  these  ventricles  will 
be  made  clear  by  reference  to  the  embryonic  brain  (Fig.  1 7)  and 
by  the  study  of  the  gross  structures  revealed  in  the  sections  of 
the  fore-brain. 

Internal  Capsule  (Capsula  Interna) . — Looking  at  the  base  of 
the  brain  we  see  two  broad  bands  of  nerve  fibers,  the  bases 
pedunculi,  issue  from  the  cerebral  hemispheres  under  cover  of 
the  optic  tracts  and,  converging  downward  and  backward,  dis- 
appear in  the  pons  (Figs.  21  and  57).  Traced  in  their  reverse 
direction,  the  fibers  of  each  basis  pedunculi  enter  the  hemisphere 
of  the  cerebrum  and  are  reinforced  by  a  great  number  of  addi- 
tional fibers  from  the  thalamus.  The  fibers  then  radiate  toward 
the  cerebral  cortex  in  the  form  of  a  hollow  cone  or  funnel,  this 
funnel-like  group  of  fibers  is  the  internal  capsule  (Fig.  40).  The 
bell  of  the  funnel  opens  upward  and  outward  and  contains  the 
lentiform  nucleus;  its  solid  spout,  directed  toward  the  pons  and 
medially,  is  the  basis  pedunculi.  Antero-inferiorly  the  fibers 
in  the  bell  of  the  funnel  diverge  to  opposite  sides  of  the  fissura 
cerebri  lateralis  (Sylvii)  and  produce  a  break  in  its  continuity, 
the  hiatus  capsulce;  otherwise  the  funnel  is  complete.  As  the 
internal  capsule  proceeds  into  the  hemisphere,  it  impales  the 
corpus  striatum  in  such  manner  as  to  place  the  caudate  nucleus 


lOO  THE    CEREBRUM 

upon  its  circumference  and  to  inclose  within  its  walls  (to  cap- 
sulate)  the  lentiform  nucleus.  The  lentiform  nucleus  is  sepa- 
rated externally  from  the  claustrum  by  a  thin  layer  of  fibers 
called  the  external  capsule. 

The  internal  capsule  is  directed  obliquely  outward  and  up- 
ward and  is  flattened  from  above  downward.  It  has,  therefore, 
a  superior  and  an  inferior  lamina  which  posteriorly,  are  con- 
tinuous with  each  V  other,  but  anteriorly  are  separated  by  the 
hiatus  capsulae.  In  horizontal  section  the  superior  lamina 
presents  a  sharp  angle,  the  genu,  directed  toward  the  median 
plane,  which  divides  the  lamina  into  an  occipital  and  a  frontal 
part. 

The  inferior  lamina  (or  inferior  ramus  as  seen  in  sagittal 
section)  is  thick  behind  but  bevels  down  to  a  sharp  edge 
anteriorly  (Figs.  39,  40,  and  93).  In  front  it  presents  a  free 
border.  Its  fibers  pass  beneath  the  lentiform  nucleus.  The 
inferior  lamina  of  the  internal  capsule  is  made  up  of  three 
composite  funiculi,  the  ventral  stalk  of  the  thalamus,  the  strio- 
fugal  fibers  and  the  upper  segment  of  the  temporo-pontal  tract. 
In  the  anterior  part  of  the  lamina,  in  front  of  a  transverse 
plane  cutting  the  mammillary  bodies,  the  ventral  stalk  of  the 
thalamus,  or  ansa  peduncularis,  and  the  strio-fugal  tracts  are 
located.  The  ventral  stalk  is  divided  by  the  nucleus  inter- 
ansalis  into  a  superior  and  an  inferior  stratum.  The  superior 
stratum  is  the  ansa  lenticularis,  which  has  both  terminal  and 
genetic  relations  with  the  lentiform  nucleus;  the  inferior  stratum 
is  called  the  inferior  peduncle  of  the  thalamus.  Both  strata  of  the 
ventral  stalk  contain  afferent  and  efferent  fibers. 

The  strio-fugal  tracts  are  intermingled  with  the  ventral  stalk 
of  the  thalamus.  They  comprise  four  sets  of  fibers,  viz.,  the 
strio-thalamic,  strio-rubral,  strio-hypothalamic  and  strio-nigral, 
which  rise  in  the  globus  pallidus  and  terminate,  respectively,  in 
the  thalamus,  nucleus  ruber,  nucleus  hypothalamicus  and 
substantia  nigra. 

The  temporo-pontal  tract  extends  from  the  temporal  cortex 
downward  to  the  nucleus  of  the  pons;  perhaps  a  few  fibers 
go  to  the  motor  nuclei  of  cranial  nerves.     The  temporo-pontal 


INTERNAL   CAPSULE  lOI 

path  is  situated  inferior  to  the  posterior  end  of  the  lentiform 
nucleus  and  behind  a  frontal  plane  cutting  the  mammillary 
bodies. 

The  retro -lentiform  part  of  the  internal  capsule  is  that  part 
of  the  superior  lamina  which  bends  down  behind  the  lentiform 


Fig.  37. — Transverse  section  of  the  brain,  directed  from  the  pons  obliquely 
upward  and  forward,  showing  internal  capsule,  corpus  callosum,  ganglia  and 
ventricles  of  the  fore-brain.     {Original.) 

a.  Callosal  sulcus,  bb.  Chorioidal  fissure,  c.  Hippocampal  fissure,  d.  Collateral 
fissure,  ee.  Inferior  horn  of  lateral  ventricle.  _  f.  Third  ventricle,  g.  Fossa  interjje- 
duncularis.  h.  Caudate  nucleus,  hh.  Cauda,  i.  Stria  terminalis.  j.  Body  of  fornix. 
jj.  Crus  of  fornix,  k.  Red  nucleus.  1.  Hypothalamic  nucleus,  m.  Substantia  nigra. 
o.  Hippocampus,     p.  Dentate  fascia,     r.  Claustrum. 

nucleus  and  joins  the  inferior  lamina.  In  the  retro-lentiform 
region  the  special  sense  tracts  are  located,  the  acustic,  the 
optic  and  probably  the  gustatory. 

The  acustic  radiation  is  the  most  inferior  of  the  three  special 
sense  tracts.  It  is  composed  of  thalamo-temporal  fibers  (audi- 
tory),  which   run   from   the   medial   geniculate   body   to   the 


I02  THE    CEREBRUM 

transverse  and  superior  temporal  gyri,  and  of  temporo-thalamic 
fibers  (reflex),  which,  in  an  inverse  direction,  connect  those 
gyri  with  the  medial  geniculate  body  and  the  inferior  quadrigem- 
inal  colliculus. 

Above  the  acustic  radiation  in  the  retro-lentiform  part 
of  the  capsule,  the  optic  radiation  is  located.  It  is  also  a  two- 
way  funiculus.  It  connects  the  thalamus  with  the  visual  cortex 
along  the  calcarine  fissure  in  the  occipital  lobe. 

The  gustatory  tract  has  not  been  definitely  located.  Prob- 
ably it  is  situated  anterior  to  the  optic  radiation,  between 
that  and  the  parietal  stalk  of  the  thalamus.  In  accord  with 
Sir  Victor  Horsley^s  tracing  of  the  gustatory  path  up  through 
the  mid-brain  to  the  dorso-medial  part  of  the  lateral  nucleus  of 
the  thalamus,  the  radiation  should  rise  in  the  thalamus  and  run 
through  the  capsule  to  the  taste  cortex,  probably,  in  the  gyrus 
cinguli  just  behind  the  splenium  of  the  corpus  callosum. 

The  parietal  stalk  of  the  thalamus  is  the  common  sensory 
tract  of  the  capsule.  It  is  located  in  front  of  the  special  tracts 
in  the  occipital  part  of  the  superior  lamina.  Anteriorly, 
its  fibers  intermingle  with  the  posterior  fibers  of  the  pyramidal 
tract.  The  corticipetal  fibers  of  the  parietal  stalk  rise  in  the 
thalamus  and  end  almost  wholly  in  the  posterior  central  gyrus; 
a  few  go  to  the  anterior  central  and  perhaps  to  the  middle  of 
the  gyrus  cinguli.  They  carry  all  kinds  of  common  sensory 
impulses  excepting  those  giving  rise  to  pleasure  and  pain. 
The  latter  impulses  induce  their  appropriate  sensations  in  the 
thalamus  (Head  and  Holmes) . 

The  pyramidal  tract,  or  cerebrospinal  tract,  is  the  voluntary 
motor  tract  contained  in  the  internal  capsule.  It  is  situated 
in  the  genu  and  the  adjacent  portion  of  the  pars  occipitalis, 
anterior  to  the  parietal  stalk  of  the  thalamus  and  between  the 
thalamus  and  the  lentiform  nucleus.  By  its  position  in  the 
capsule  the  pyramidal  tract  is  divided  into  a  genicular  and  an 
occipital  part.  Both  parts  rise  in  the  motor  cortex  of  the 
anterior  central  and  paracentral  gyri,  and  terminate  in  con- 
nection with  the  nuclei  of  all  motor  nerves;  the  part  in  the  genu 
goes  to  the  motor  nuclei  of  cranial  nerves,  the  occipital  part  to 


TRACTS   IN   CAPSULE  IO3 

the  motor  nuclei  of  spinal  nerves.  The  pyramidal  tract  con- 
ducts voluntary  motor  impulses  and  inhibitory  impulses. 

Among  the  fibers  of  the  pyramidal  tract,  behind  the  genu 
of  the  capsule,  there  is  a  small  tract  described  by  von  Monakow, 
which  rises  in  the  opercular  region  of  the  frontal  lobe  and  ter- 
minates in  the  red  nucleus.  It  is  the  cerebrorubral  tract 
{tractus  cerebrorubricus) . 

The  pars  frontalis  of  the  internal  capsule  contains  two 
tracts  and  a  large  number  of  internuncial  fibers  connecting 
the  nuclei  of  the  striate  body. 

The  internuncial  fibers  freely  associate  the  caudate  nucleus 
and  the  putamen  of  the  lentiform  nucleus,  and  the  caudate 
and  globus  pallidus.  It  is  through  the  thalamus  that  the 
striate  body  is  connected  with  the  cerebral  cortex  (A.  S. 
Kinnier  Wilson) . 

Fronto-pontal  Tract.^ — The  upper  part  of  the  fronto-pontal 
tract  and  the  frontal  stalk  of  the  thalamus  are  intermingled 
with  one  another  in  the  frontal  part  of  the  capsule.  The  fronto- 
pontal  tract  rises  in  the  posterior  and  middle  parts  of  the  three 
frontal  gyri;  it  descends  to  the  nucleus  of  the  pons  and  per- 
haps to  the  motor  nuclei  of  cranial  nerves. 

The  frontal  stalk  of  the  thalamus  originates  in  the  lateral 
nucleus  of  the  thalamus.  It  issues  from  the  anterior  part 
of  the  nucleus  and,  running  through  the  frontal  part  of  the  cap- 
sule, terminates  in  the  caudate  nucleus  and  in  those  parts  of 
the  frontal  gyri  in  which  the  fronto-pontal  tract  takes  its 
origin.  This  is  an  afferent  tract,  conducting  impulses  to  the 
caudate  nucleus  and  frontal  cortex;  but  it  is  probably  not  a 
sensory  tract. 

Disregarding  for  the  moment  the  direction  of  growth  and 
conduction,  we  may  say  that  the  fibers  of  the  internal  capsule 
radiate  toward  the  cortex  as  soon  as  the  striate  body  is  passed; 
they  form  the  capsular  radiation;  and,  together  with  the  radia- 
tion of  the  corpus  callosum,  they  form  the  corona  radiata, 
which  is  shown  in  frontal  sections  of  the  cerebrum  cutting  the 
capsule  and  callosum. 

Many  fibers  of  the  internal  capsule  give  off  branches  (col- 


I04  THE    CEREBRUM 

laterals)  which  pass  through  the  corpus  callosum  to  the  oppo- 
site hemisphere;  other  fibers  may  be  traced  entire  through  the 
same  course  to  the  cortex  of  the  opposite  side.  A  bundle  of 
thalamic  fibers  has  been  so  traced  (Hamilton) . 

The  superior  lamina  of  the  internal  capsule,  proceeding  out- 
ward and  upward  into  the  hemisphere,  intermingles  with  the 
corpus  callosum  and  enters  into  the  corona  radiata.  Together 
with  the  caudate  nucleus,  thalamus  and  stria  terminalis (taenia 
semicircularis) ,  which  lie  on  its  medial  surface,  it  forms  the 
entire  lateral  boundary  of  the  general  cavity  of  the  fore-brain. 

Corpus  Callosum  (Figs.  35,  37,  42  and  54). — The  entire  roof 
of  the  fore-brain  cavity,  representing  the  base  of  the  wedge,  is 
formed  by  the  corpus  callosum.  A  part  of  the  anterior  bound- 
ary is  also  fomed  by  it.  The  corpus  callosum  is  a  thick  sheet  of 
fibers  four  and  a  half  inches  broad,  from  before  backward,  which 
joins  the  hemispheres  together.  It  constitutes  the  great  com- 
missure, being  composed  chiefly  of  those  medullated  cortical 
axones  which  end  in  arborizations  about  cortical  cells  of  the 
opposite  hemisphere.  It  contains  some  fibers  which  belong  to 
the  internal  capsule;  and,  also,  collaterals  from  capsular  and 
association  fibers.  The  corpus  callosum  is  placed  nearer  to  the 
anterior  than  the  posterior  pole  of  the  hemispheres.  Separat- 
ing the  hemispheres  above,  it  is  seen  in  the  bottom  of  the 
longitudinal  fissure.  It  is  about  an  inch  in  transverse  length  at 
the  posterior  end. 

The  upper  surface  is  concave  from  side  to  side  and  divided 
in  the  median  line  by  a  longitudinal  raphe  (Figs.  37  and  42). 
Transverse  striae  are  plainly  visible.  Two  longitudinal  striae 
are  also  found  running  on  either  side  of  the  raphe;  one  next  the 
raphe,  the  medial  longitudinal  stria;  and  the  other  near  the 
lateral  end  of  the  callosum,  the  lateral  longitudinal  stria.  The 
medial  and  lateral  longitudinal  striae  are  imbedded  in  a  thin 
sheet  of  gray  substance,  the  stratum  indusium  griseum;  alto- 
gether they  constitute  the  gjorus  supracallosus.  If  traced 
around  the  posterior  border  of  the  callosum,  this  supracallosal 
gyrus  is  found  to  be  continuous  with  the  fasciola  cinerea  and 
gyrus  subsplenialis  and  through  them  with  the  fascia  dentata. 


CALLOSAL   GYRI 


105 


Io6  ■  THE    CEREBRUM 

The  gyrus  supracallosus  becomes  the  gyrus  subcallosus 
{peduncle  of  corpus  callosum)  and  area  parolfactoria  after  it 
winds  around  the  anterior  border  of  the  corpus  callosum. 
The  gyrus  subcallosus  is  continued  downward  between  the  lamina 
terminalis  and  the  posterior  parolfactory  sulcus  to  the  base  of 
the  cerebrum,  and  then,  as  gyrus  diagonalis,  across  the  anterior 
perforated  substance  to  the  uncus.  At  the  anterior  and  at 
the  posterior  border,  the  corpus  callosum  is  bent  down- 
ward (scroll-like);  hence,  it  is  superiorly  convex  from  before 
backward. 

Its  inferior  surface  forms  the  roof  of  the  lateral  ventricles 
(Figs.  35  and  37).  It  is  concave  antero-posteriorly  and  near 
its  posterior  border  is  fused  with  the  body  of  the  fornix.  An- 
terior to  that  fusion  it  is  joined  to  the  fornix  along  the 
median  line  by  the  septum  pellucidum. 

The  posterior  border  (Fig.  35)  is  flexed  downward  from  the 
horizontal  about  forty-five  degrees.  Giving  passage  to  the 
fibers  which  join  the  middle  and  posterior  parts  of  the  hemi- 
spheres, the  posterior  border  is  the  thickest  part  of  the  corpus 
callosum.  It  is  on  that  account  called  the  pad,  or  splenium, 
A  large  bundle  of  these  splenial  fibers  arches  back  toward  the 
medial  surface  of  the  occipital  lobe;  they  form  the  forceps 
major. 

The  anterior  border  is  bent  downward  and  then  backward 
sweeping  through  180  degrees  of  flexion  (Fig.  35).  It  tapers 
down  to  a  sharp  edge  called  the  rostrum.  A  very  thin  sheet-like 
extension  of  the  rostrum,  called  the  lamina  rostralis,  proceeds 
backward  from  the  beak  and  becomes  continuous  with  the 
lamina  terminalis.  The  transverse  fibers  of  the  rostrum  in 
the  hemisphere  form  the  floor  of  the  anterior  horn  of  the  lateral 
ventricle.  Running  downward  on  either  side  of  the  rostrum 
is  a  low  ridge,  continuous  with  the  stria  longitudinalis  medialis, 
which  constitutes  the  gyrus  subcallosus.  Each  gyrus  sub- 
callosus, after  passing  across  the  anterior  perforated  substance, 
ends  in  the  uncus  of  the  hippocampal  gyrus. 

Genu  and  Truncus  (Fig.  35). — The  down- turned  anterior  part 
of  the  corpus  callosum  is  the  genu.     It  joins  the  rostrum  to  the 


CORPUS   CALLOSUM  I07 

main  body,  the  truncus.  The  genu  forms  part  of  the  anterior 
boundary  of  the  cerebral  cavity;  the  truncus  forms  the  roof. 
Fibers  uniting  the  frontal  lobes  of  the  cerebrum  pass  through 
the  genu,  and  in  the  hemisphere,  bound  the  anterior  horn  of  the 
lateral  ventricle  above  and  in  front.  Those  fibers  arching  for- 
ward and  forming  the  roof  of  the  anterior  horn  are  called  the 
forceps  minor.  The  forceps  major,  composed  of  fibers  from  the 
splenium  which  bend  backward  into  the  occipital  lobe,  lies  in  the 
roof  and  inner  wall  of  the  posterior  horn  and  produces  the 
eminence  called  the  hulh  (Fig.  49). 

Each  lateral  extremity  of  the  corpus  callosum  is  overhung  by 
the  gyrus  cinguli,  which  covers  the  lateral  longitudinal  stria. 
Inclosed  between  the  gyrus  cinguli  and  corpus  callosum  is  the 
callosal  fissure  (ventricle  of  the  callosum) .  The  lateral  extremity 
of  the  corpus  callosum,  within  the  cerebral  hemisphere,  inter- 
mingles with  the  superior  lamina  of  the  internal  capsule  and 
thus  stretches  entirely  across  the  fore-brain  cavities  (Figs.  37 
and  54). 

The  boundaries  of  the  general  cavity  of  the  fore-brain  may  be 
given  as  follows: 
Roof  (base  of  wedge) — 

Corpus  callosum.  ' — 

Floor  (edge  of  wedge) — 

Tegmenta  of  mid-brain, 

Posterior  perforated  substance  of  mid-brain, 

Tuber  cinereum, 

Infundibulum, 

Optic  chiasma. 
Lateral  wall  (beveled  surface) — 

Internal  capsule  (superior  lamina). 

Caudate  nucleus. 

Stria  terminalis. 

Thalamus. 
Anterior  wall  (border  of  wedge) — 

Lamina  terminalis. 

Anterior  commissure, 

Genu  of  corpus  callosum. 


I08  "  THE    CEREBRUM 

Posterior  wall — 

Posterior  commissure  with  cerebral  aqueduct  beneath  it, 

Pineal  body, 

Corpora  quadrigemina  of  mid-brain, 

Transverse  fissure  of  cerebrum,  containing  the  chorioid  tela 
of  third  ventricle, 

Splenium  of  corpus  callosum. 

The  fore-brain  cavity  thus  bounded  is  subdivided  by  two 
partitions  (Figs.  35,  46  and  54).  The  body  of  the  fornix, 
together  with  the  chorioid  tela  of  the  third  ventricle  and  the  roof 
epithelium  of  the  third  ventricle,  forms  a  horizontal  partition 
which  divides  the  cavity  into  an  upper  and  lower  chamber.  The 
superior  chamber  is  divided  into  two  lateral  chambers,  the 
lateral  ventricles,  by  a  double  vertical  partition,  the  septum 
pellucidum.     The  inferior  chamber  is  the  third  ventricle. 

The  body  of  the  fornix  {corpus  fornicis,  Figs.  35  and  47)  is 
a  triangular  sheet  of  fibers,  whose  base  is  attached  to  the  under 
surface  of  the  splenium  of  the  corpus  callosum,  and  whose  bifid 
apex  extends  forward  to  the  rostrum  and  the  anterior  com- 
missure. Its  lateral  borders  rest  on  the  thalami,  the  chorioid 
tela  alone  intervening  (Fig.  54).  And  the  narrow  chamber 
between  the  thalami,  the  third  ventricle,  is  separated  from  the 
broader,  superior  part  of  the  fore-brain  cavity  by  the  body  of  the 
fornix  together  with  the  chorioid  tela  and  layer  of  epithelium. 
The  body  of  the  fornix  is  produced  by  the  approximation  of  two 
bundles  of  white  fibers,  one  belonging  to  each  hemisphere. 
These  bundles  are  the  crura  of  the  fornix. 

The  cms  fornicis  (Figs.  35,  43  and  49)  may  be  traced  from 
the  uncus  and  the  hippocampus,  its  chief  origin,  upward  through 
the  inferior  horn  and  into  the  floor  of  the  body  of  the  lateral 
ventricle,  where  it  unites  with  its  fellow  of  the  opposite  side  in 
forming  the  body  of  the  fornix.  At  the  apex  of  the  body  of  the 
fornix,  which  is  the  anterior  end,  the  bundles  again  separate  and 
become  the  columnae  of  the  fornix.  The  crura  are  united  at  the 
back  part  of  the  body  of  the  fornix  by  a  few  transverse  and 
oblique  fibers  which  form  the  lyre,  or  commissura  hippocampi 
(Fig.    47).     The   commissure   is   best   seen   when   the   corpus 


FORNIX  109 

callosum  and  fornix  .are  viewed  from  below;  its  fibers  connect 
each  crus  of  the  fornix  with  the  hippocampus  and  uncus  of  the 
opposite  side. 

The  columnae fomicis  (Figs.  35,  50  and  51),  one  on  either  side 
pass  down  in  front  of  the  thalami,  bounding  the  foramina  inter- 
ventricularia  (Monroi);  and  then  descend  to  the  corpora 
mammillaria,  at  the  base  of  the  brain.  On  the  way  down  the 
free  part  of  each  columna  {pars  libera)  passes  behind  the 
anterior  commissure,  beyond  which  (as  pars  tecta)  it  pierces  the 
inner  part  of  the  thalamus  of  the  same  side.  The  fibers  of  the 
columna  fornicis  for  the  most  part  terminate  in  the  medial 
^nucleus  of  the  corpus  mammillare,  from  which  other  fibers  take 
their  origin,  forming  the  fasciculus  mammillaris  princeps.  This 
bundle  divides  Y-like;  the  anterior  branch  is  the  fasciculus 
mammillo-thalamicus  (Vicq  d^Azyri)  and  ascends  to  the 
anterior  nucleus  of  the  thalamus;  the  posterior  bundle  is  the 
fasciculus  mammillo-tegmentalis  and  probably  ends  in  the 
stratum  griseum  centrale  and  nucleus  tegmenti  profundus  of 
the  mid-brain. 

At  the  lower  border  of  the  interventricular  foramen  a  small 
bundle  of  fibers  leaves  the  columna  of  the  fornix;  this  is  rein- 
forced by  fibers  from  the  anterior  perforated  substance  and 
septum  pellucidum  and,  bending  backward,  runs  as  medullary 
stria  along  the  thalamus  to  the  nucleus  of  the  habenula;  some  of 
the  fibers  decussate  through  the  stalk  of  the  pineal  body  to  the 
opposite  nucleus  habenulae  and  constitute  the  commissura 
hahenularum.  The  columna  of  the  fornix  is  joined  by  a  small 
fasciculus  from  the  intermediate  stria  of  the  olfactory  tract, 
which  runs  backward  to  the  hippocampus  and  uncus. 

The  upper  surface  of  the  body  of  the  fornix  is  convex  from 
before  backward  (Figs.  35  and  47) .  It  forms  the  postero-medial 
part  of  the  floor  of  the  lateral  ventricle.  Along  the  median  line 
it  is  joined  to  the  corpus  callosum  by  the  septum  pellucidum. 

The  septum  pellucidum  (Figs.  35,  46,  50  and  96),  a  double- 
walled  median  partition,  divides  the  superior  chamber  of  the 
fore-brain  cavity  into  lateral  halves,  the  lateral  ventricles.  The 
septum  pellucidum  is  crescentic  in  outline.     Its  convex  border 


no  THE   CEREBRUM 

fits  into  the  concave  surface  of  the  body,  genu  and  rostrum  of  the 
corpus  callosum.  Its  concave  border  rests  upon  the  fornix. 
Between  the  rostrum  of  the  corpus  callosum  and  the  anterior 
commissure,  the  septum  pellucidum  is  continuous  with  the  gyrus 
subcallosus  with  which  it  is  associated  in  development  and 
function. 

The  septum  pellucidum,  like  the  anterior  commissure,  corpus 
callosum  and  fornix,  is  developed  from  the  thickened  upper 
border  of  the  lamina  terminalis  and  the  adjacent  medial  wall  of 
the  cerebral  hemisphere  in  front  of  the  interventicular  foramen. 
These  several  structures  extend  upward  and  backward  with  the 
development  and  rotation  of  the  hemispheres  and  together 
roof  over  the  inter-brain.  A  lymph  space,  the  cavum  sepii 
pellucidi,  appears  in  the  septum  and  is  commonly  called  the 
fifth  ventricle.  The  fore-brain  cavity  thus  embraces  four 
ventricles,  viz.: 

Two  lateral  ventricles  (the  ventricles  of  the  hemispheres), 
Cavum  septi  pellucidi  (the  ventricle  of  the  septum),  and 
Third  ventricle  (ventricle  of  the  inter-brain) . 

CAVUM  SEPTI  PELLUCIDI 

This  is  the  cavity  of  the  septum  but  not  a  true  ventricle,  as  it 
was  never  any  part  of  the  venter  of  the  neural  tube.  The 
cavity  of  the  septum  is  a  very  narrow,  antero-posterior  cleft 
between  the  walls  of  the  septum  pellucidium,  with  which  it 
coincides  in  extent.  It  is  situated  within  the  concavity  of  the 
corpus  callosum  between  the  lateral  ventricles,  above  and 
anterior  to  the  third  ventricle.  Below  and  posteriorly  it  is 
bounded  by  the  fornix.  It  is  not  a  part  of  the  embryonic  brain 
cavity,  but  a  mere  lymph  space.  Therefore  it  does  not  com- 
municate with  any  other  ventricle,  each  of  the  others  being  a 
part  of  the  cavity  of  the  neural  tube  from  which  both  brain  and 
cord  are  developed.  Instead  of  ependyma,  which  lines  other 
ventricles,  the  lining  of  the  fifth  is  endothelium.  A  lymph-like 
fluid  fills  it. 


VENTRICLES  III 

THE  LATERAL  VENTRICLE 

(Ventriculus  Lateralis) 

The  hemispheres  contain  the  largest  of  the  six  ventricles 
(Figs.  37,  46,  53,  54  and  96).  Situated  one  on  either  side  of 
the  median  line,  the  ventricles  of  the  hemispheres  are  very 
naturally  called  the  lateral  ventricles.  Each  represents  a 
branch  of  the  cavity  of  the  embryonic  neural  tube  (Figs.  17  and 
53).  In  consequence,  the  lateral  ventricles  communicate 
with  all  others  except  the  fifth.  By  the  interventricular  fora- 
men (of  Monro),  each  directly  communicates  with  the  third 
ventricle;  and  through  that,  indirectly,  with  the  fourth  and 
sixth.  The  foramen  interventriculare  is  situated  between 
the  front  of  the  thalamus  and  the  calumna  of  the  fornix  (Fig. 
35).  It  extends  between  the  anterior  extremity  of  the  third 
ventricle  (the  aula)  and  the  junction  of  the  anterior  horn  with 
the  central  part  of  the  lateral  ventricle.  The  lateral  ventricles 
are  lined  with  ependyma,  which  is  a  transparent  membrane 
composed  of  two  layers  when  complete,  viz.,  neuroglia  and  a 
covering  of  columnar  ciliated  epithelial  cells.  Over  the  thala- 
mus (the  part  seen  in  the  lateral  ventricle)  and  the  chorioid 
plexus,  the  neurogliar  layer  is  absent. 

The  ventricles  are  filled  with  a  displaceable  liquid,  called 
the  cerebrospinal  fluid.  This  fluid  is  secreted  by  the  epithelial 
cells  of  the  chorioid  plexuses  and  constantly  flows  out  into  the 
subarachnoid  spaces;  it  escapes  through  the  medial  wall 
of  the  inferior  horn  of  the  lateral  ventricle  and  the  roof  of  the 
fourth  ventricle.  The  whole  amouut  of  cerebrospinal  fluid 
is  said  to  average  from  100-130  cc;  but  in  any  individual  it 
varies  inversely  as  the  brain-mass ;  with  increased  blood  supply 
or  hemorrhage  or  tumor  growth  in  the  brain,  the  amount  of 
fluid  is  diminished  so  that  dangerous  pressure  will  not  be 
exerted  upon  the  delicate  brain  tissues.  Varied  function  is 
thus  made  possible  and  often  life  is  preserved.  The  ancients 
considered  the  ventricles  the  abode  of  the  soul. 

The  lateral  ventricle  may  be  studied  best  in  four  parts:  the 
central  part  (or  body);  the  anterior  horn;  the  inferior  horn;  and 
the  posterior  horn. 


112 


THE    CEREBRUM 


STRIATED   BODY  flnHHV^S 


The  central  part  of  the  lateral  ventricle  (Figs.  45,  47  and  50) 
is; the  ventricle  of  the  parietal  lobe  of  the  cerebrum.     The 
following  are  its  boundaries : 
Roof — Corpus  callosum. 
Floor  (from  before,  backward  and  inward) — 

Caudate  nucleus  of  the  corpus  striatum, 

Vena  terminalis  and  stria  terminalis  (taenia  semicircularis), 

Thalamus  (covered  by  epithelium), 

Lamina  chorioidea  epithelialis  and  chorioid  plexus, 

Fornix. 
Medial  wall — Septum  pellucidum. 
Lateral  wall — Internal  capsule. 


Fig.  40. — Diagram  of  right  internal  capsule  in  colors.     {Original.) 
Red,  motor;  Blue,  common  sensory;  Purple,  special  sensory. 

The  corpus  callosum  forms  a  complete  roof  for  the  central 
part  of  the  lateral  ventricle.  The  roof  inclines  upward  and 
outward  from  the  septum  pellucidum,  the  inner  wall  of  the 
ventricle,  to  the, superior  lamina  of  the  internal  capsule,  which 
forms  its  outer  wall.  The  floor  of  the  central  part  of  the 
ventricle  is  formed  by  the  six  parts,  as  named  above,  which 
will  now  be  considered  in  the  order  given. 

Corpus  Striatum  (Figs.  37,  38,  39  and  41). — The  striated 
body  is  the  basal  ganglion  of  the  hemisphere.  It  is  an  ovoid 
mass  of  gray  matter  imbedded,  for  the  most  part,  in  the  cerebral 
8 


114  THE   CEREBRUM 

medulla ;  but  it  is  continuous  below  with  the  anterior  perforated 
substance,  and  extends  above  to  the  lateral  ventricle.  It 
measures  6.3  cm.  (2.5  in.)  from  before  backward,  3.1  cm. 
(1.25  in.)  transversely,  and,  from  above  downward,  3.7  cm. 
(1.5  in.).  It  is  placed  anterior  and  lateral  to  the  thalamus 
and  forms  the  third  of  the  great  divisions  of  the  cerebral 
hemisphere,  viz.,  the  neopallium,  the  rhinencephalon  and  the 
corpus  striatum.  It  is  a  reddish-gray  body,  and  its  streaked 
appearance  is  due  to  the  white  capsular  fibers  which  pierce  it. 
Embryologically  the  corpus  striatum  is  built  up  of  several 
nuclei  which  appear  in  man  in  the  order  of  their  philogenetic 
origin;  first,  the  globus  pallidus  of  the  lentiform  nucleus,  the 
only  part  found  in  fishes;  second,  the  nucleus  amygdalcB;  and, 
third,  the  caudate  nucleus  and  putamen  of  the  lentiform  nucleus. 
The  last  three  are  first  developed  in  reptiles  and  birds.  In 
the  mature  human  brain  the  caudate  and  lentiform  nuclei  are 
easily  distinguished,  being  separated  by  the  internal  capsule;  but 
the  amygdala  has  no  definite  boundary  and  forms  the  antero- 
inferior part  of  the  striate  body  where  the  capsule  does  not 
divide  it.  This  undivided  part  of  the  corpus  striatum  is 
continuous  with  the  uncus,  the  anterior  perforated  substance 
and  the  claustrum.  The  amygdala,  which  forms  a  part  of 
the  uncus,  is  a  reflex  center  of  the  rhinencephalon.  The 
globus  pallidus,  assisted  by  the  putamen  and  caudate  nucleus, 
constitutes  an  autonomous  organ  to  steady  the  action  of  the 
lower  motor  neurones,  preventing  hypertonicity,  rigidity  and 
tremor  (S.  A.  Kinnier  Wilson). 

The  lentiform  nucleus  {nucleus  lentiformis)  occupies  the 
cone-hke  cavity  of  the  internal  capsule,  by  whose  laminae  it  is 
separated  from  the  ventricle  (Fig.  39).  It  is  shorter  fore  and 
aft  than  the  caudate  nucleus.  It  resembles  a  biconvex  lens  with 
a  somewhat  thickened  anterior  border,  when  viewed  in  hori- 
zontal section  (Fig.  38).  In  transverse  vertical  section  through 
its  center,  it  is  triangular  in  shape.  The  hypotenuse  and  base 
are  formed,  respectively,  by  the  superior  and  inferior  laminae 
of  the  internal  capsule.  The  external  capsule  forms  the  per- 
pendicular   and    separates    the    lentiform    nucleus    from    the 


STRIATED  BODY 


115 


claustrum.  The  latter  is  a  thin  sheet  of  isolated  gray  matter, 
found  just  medial  to  the  island  (of  Reil).  In  extent  and  posi- 
tion, fore  and  aft,  the  island  and  lentiform  nucleus  coincide. 
The  lentiform  nucleus  is  subdivided  by  two    white   laminae, 


Fig.  41. — Brain-stem  viewed  from  the  left  side;  internal  capsule  in  colors. 

a.  Pulvinar  of  thalamus,  b.  Pineal  body.  c.  Superior  colliculi  of  quadrigeminal  body- 
d.  Inferior  colliculi.  e.  Lateral  fillet,  f.  Brachia  conjunctiva,  g.  Ventral  spino-cere. 
bellar  tr.  winding  over  brachium  conjunctivum. 


parallel  with  its  external  surface,  into  three  zones.  (Fig. 
37).  The  outer  zone,  called  the  putamen,  is  deeply  pigmented, 
and,  like  the  caudate  nucleus,  is  of  a  reddish-gray  color;  but 
the  two  inner  zones,  having  less  pigment,  are  of  a  pale  yellowish 


ii6 


THE    CEREBRUM 


tint.     They  form  the  globus  pallidus.     Anterior  to  the  capsular 
laminae  the  lentiform  nucleus  fuses,  in  front,  with  the  caudate 
nucleus  and,  below,  with  the  nucleus  amygdalae. 
,    The  nucleus  caudatus  (the  tailed  nucleus)  is  a  pear-shaped 


Fig.  42. — Dorsal  surface  of  corpus  callosum,  cerebral  hemisphere  cut  away  to 
expose  it.     {Original.) 

body  of  reddish-gray  color,  situated  on  the  perimeter  of  the 
internal  capsule  (Figs.  37,  41  and  50).  It  is  the  intraventricular 
part  of  the  striated  body  and  forms  a  strip  of  the  ventricular 
floor  along  the  outer  wall.     The  head  {caput)  of  the  caudate 


VENTRICULAR   FLOOR  II7 

nucleus  is  directed  forward.  It  is  seen  in  the  anterior  horn  of 
the  lateral  ventricle.  From  the  head  the  nucleus  tapers  as  it 
proceeds  backward  through  the  central  part  of  the  ventricle. 
Its  tail  (cauda)  turns  downward  in  the  roof  of  the  inferior  horn, 
and  ends  in  the  nucleus  amygdalce,  while  the  head  of  the  caudate 
nucleus  fuses  with  the  lentiform  nucleus  (Fig.  41).  The 
caudate  nucleus  is  covered  on  its  ventricular  surface  by  epen- 
dyma.  The  opposite  surface,  resting  against  the  fibers  of  the 
internal  capsule,  is  irregular  and  serrated. 

Along  the  ventricular  floor  the  sulcus  intermedius  prosen- 
cephali  separates  the  caudate  nucleus  from  the  thalamus. 

The  nucleus  amygdalae  is  the  most  inferior  part  of  the 
striate  body.  It  forms  that  part  of  the  uncus  anterior  to  the 
pars  transversa  of  the  dentate  fascia  and  behind  the  rudimen- 
tary gyri  circumambiens  and  semilunaris.  Superiorly  it  merges 
with  the  lentiform  nucleus;  posteriorly  it  joins  the  tail  of  the 
caudate  nucleus  and  receives  the  stria  terminalis,  an  olfactory 
fasciculus  from  the  anterior  perforated  substance  and  septum 
pellucidum.  The  amygdalate  nucleus  constitutes  a  reflex 
center  in  which  olfactory  impulses  excite  the  mechanism  regulat- 
ing movement  (S.  A.  K.  Wilson). 

The  stria  terminalis  (taenia  semicircularis,  Figs.  37  and  47) 
lies  just  medial  to  the  nucleus  caudatus  in  the  sulcus  intermedius. 
It  is  a  band  of  white  fibers  traversing  the  floor  of  the  central 
part  of  the  ventricle  and  the  roof  of  its  inferior  horn,  but  covered 
by  the  terminal  vein  and  by  the  ependyma.  The  terminal 
vein  is  easily  seen,  but  the  stria  terminalis  is  of  microscopic 
size.  The  terminal  vein  and  terminal  stria  are  so  called  because 
they  follow  the  boundary  between  the  end-brain  and  the  inter- 
brain.  The  stria  terminalis  rises  in  the  anterior  perforated 
substance  and  the  septum  pellucidum;  it  partially  decussates; 
in  the  anterior  commissure  and  ends  in  the  nucleus  amygdalae., 
It  is  a  bundle  of  olfactory  projection  fibers.  The  vena  ter- 
minalis joins  the  chorioid  vein  and  the  vein  of  the  septum 
pellucidum  near  the  interventricular  foramen;  thus,  the 
vena  cerebri  interna  is  formed. 

The  lamina  chorioidea  epithelialis  is  a  single  layer  of  epen- 


ii8 


THE    CEREBRUM 


THALAMUS 

dymal  cells,  derived  from  the  roof -plate  of  the  telencephalon; 
it  stretches  between  the  stria  terminalis,  in  the  sulcus  inter- 
medius,  and  the  lateral  border  of  the  body  and  crus  of  the 
fornix.  Like  the  roof-plate  elsewhere  it  develops  no  neurones. 
It  invests  the  lateral  area  of  the  superior  surface  of  the  thalamus 
for  a  distance  of  4-6  mm.  and  the  part  attached  to  the  thalamus 
is  called  the  lamina  affixa.  The  medial  edge  of  the  affixed 
portion  constitutes  the  tcenia  chorioidea.  Between  the  taenia 
chorioidea  and  the  fornix  the  epithelial  lamina  is  invaginated 
into  the  lateral  ventricle,  producing  the  chorioidal  fissure. 
A  fold  of  pia  mater,  rich  in  blood-vessels,  dips  into  that  fissure 
and  forms  the  chorioid  plexus  of  the  lateral  ventricle.  The 
chorioid  epithelial  lamina  is  seen  to  be  made  up  of  two  parts: 
a  lateral  part  afiixed  to  the  thalamus  and  resembling  ependyma 
elsewhere  and  a  medial  part  investing  the  chorioid  plexus  and 
possessing  large  cubical  and  cylindrical  cells  of  specific  function. 

Thalamus  (Figs.  37,  38,  47  and  50). — A  fusiform  part  of  this 
ganglion  of  the  inter-brain  is  visible  in  the  floor  of  the  lateral 
ventricle,  between  the  stria  terminalis  and  the  chorioid  plexus. 
It  extends  throughout  the  central  part  of  the  ventricle  from  the 
interventricular  foramen  to  the  inferior  horn.  A  transparent 
layer  of  epithelium,  the  lamina  chorioidea  epithelialis,  extending 
from  the  fornix  to  the  stria  terminalis  and  representing  the  hemi- 
sphere wall,  covers  it;  and  the  part  called  lamnia  affixa  is 
attached  to  it.  The  thalamus  will  be  described  with  the 
third  ventricle  and  inter-brain. 

The  chorioid  plexus  {plexus  chorioideus,  Figs.  44,  47  and  48) 
of  the  lateral  ventricle  is  the  vascular  border  of  the  chorioid  tela 
of  the  third  ventricle.  It  projects,  laterally,  from  beneath  the 
fornix  and  its  crus  through  the  chorioidal  fissure  into  the  floor 
of  the  central  part  of  the  ventricle  and  the  inner  wall  of  the 
inferior  horn.  The  epithelium,  above  mentioned,  invests  it; 
and  it  borders  the  fornix  like  a  ruffle.  It  is  called  chorioid 
plexus  (chorion,  a  membrane)  because  it  is  membrane-like. 
At  the  junction  of  the  central  part  and  inferior  horn  of  the 
lateral  ventricle  the  chorioid  plexus  presents  a  large  skein- 
like mass  called  the  glomus  chorioideum  (Fig.  47).     The  an- 


I20 


THE    CEREBRUM 


terior  choroidal  artery  from  the  internal  carotid  and  the 
postero-lateral  chorioidal,  a  branch  of  the  posterior  cerebral, 
supply  the  plexus.  The  former  pierces  the  temporal  lobe  and 
enters  the  apex  of  the  inferior  horn  of  the  ventricle;  the  latter 
passes  in  through  the  transverse  and  chorioidal  fissures  of 
the  cerebrum,  following  the  chorioid  tela.  The  chorioidal 
vein  carries  the  blood  away.  At  the  foramen  interventricu- 
lare,  it  is  joined  by  the  terminal  vein  of  the  striated  body  and 


Chorioid  tela  of 
third  ventricle 

Tail  of  caudate 
nucleus 

Pulvinar  of 
thalamus 


Internal  capsule,.  ^^ 


Putamei 
Claustrurj 


Habenular 
nucleus 
Tail  of  caudate 
nucleus 

optic  tract 

Fimbria  of 
hippocampus 

Dentate  gyrus 

Peduncle  of 

cerebrum  ' 

Post,  recess  of 

interpeduncular 


Chorioid  plexus 
of  third  ven- 
tricle 


^^ — .Red  nucleus 


Hypothalamic 
nucleus 


Substantia 
nigra 


Fig.  44. — Coronal  section  of  brain  through 


Pons  (Varoli) 
red  nuc.     {Morris  after  Toldt.) 


the  veins  of  the  septum  pellucidum  and  forms  the  internal 
cerebral  vein.  The  internal  crebral  vein  courses  backward  in 
the  chorioid  tela  and  unites  with  its  fellow  of  the  opposite 
side  to  form  the  great  cerebral  vein,  proximal  to  which  union 
it  receives  the  basilar  vein;  and  then  the  great  cerebral  vein 
(of  Galen),  uniting  with  the  inferior  sagittal  sinus,  forms  the 
straight  sinus. 

F.  W.  Mott  calls  the  chorioid  plexuses  the  chorioid  glands. 
The  name  is  justified  by  their  structure.     The  chorioid  glands, 


INFERIOR  HORN   OF  VENTRICLE 


121 


122 


THE    CEREBRUM 


and  especially  those  of  the  lateral  ventricles,  are  made  up  of 
numerous  invaginations  of  the  chorioid  epithelial  lamina  con- 
taining loops  of  blood-vessels,  arteries  and  veins  joined  by  capil- 


Fig.  46. — Horizontal  section  of  cerebrum,  cutting  splenium  and  genu  of  corpus 
callosum,  showing  lateral  ventricles,  septum  pellucidum,  fornix  and  transverse 
temporal  gyri.     (Original.) 

lary  plexuses;  the  epithelial  cells  are  large  and  granular, 
cubical,  polygonal  or  pyramidal  in  shape  and  very  different 
from  the  adjacent  ependymal  cells;  and  around  the  vessels 
and  among  the  epithelial  cells  there  are  many  fine  nerve  fibers. 


HORNS   OF  LATERAL  VENTRICLE  1 23 

The  chorioid  plexuses  secrete  the  cerebrospinal  fluid;  and, 
according  to  the  late  Prof.  E.  E.  Goldmann,  they  exclude  many 
noxious  substances  circulating  in  the  blood  from  the  central 
nervous  system. 

The  floor  of  the  central  part  of  the  lateral  ventricle  is  com- 
pleted by  the  superior  surface  of  the  fornix. 

The  horns  of  the  lateral  ventricle  are  three  in  number;  the 
anterior,  inferior  and  posterior  (Figs.  45,  50  and  53). 

The  anterior  horn  (cornu  anterius,  Figs.  46,  47  and  96)  pro- 
jects from  the  central  part  of  the  ventricle  forward  and  out- 
ward around  the  head  of  the  caudate  nucleus.  It  is  the  ventricle 
of  the  frontal  lobe  and  is  deep  and  narrow.  Its  boundaries 
are  as  follows : 

Roof — Corpus  callosum  (forceps  minor). 

Floor — Rostrum . 

Anterior  wall — Genu. 

Inner  wall — Septum  pellucidum. 

Outer  wall — Caudate  nucleus. 

The  posterior  horn  (cornu  posterius,  Figs.  45,  46,  47,  49,  50 
and  53)  is  directed  backward  and  downward  in  a  curve  concave 
inward,  from  the  ventricular  center  into  the  occipital  lobe;  and, 
like  the  occipital  lobe,  it  first  makes  its  appearance  in  the  fifth 
month  of  embryonic  life.  Its  extremity  bends  medially  toward 
the  posterior  calcarine  fissure,  with  which  the  horn  is  parallel. 
The  anterior  calcarine  fissure  produces  the  ridge  along  the  inner 
wall  called  the  calcar  avis.  The  posterior  horn  is  roofed  over 
by  fibers  from  the  splenium  of  the  corpus  callosum,  which  turn 
down  outside  the  horn  and  also  form  part  of  the  lateral  bound- 
ary. In  the  lateral  wall  and  in  the  roof  and  floor  is  also  the 
optic  radiation.  A  well-marked  bundle  of  fibers  from  the 
splenium,  forceps  major,  is  found  passing  along  the  medial 
border  of  the  roof  into  the  occipital  lobe.  It  produces  an 
eminence  above  the  calcar  avis,  called  the  bulb.  The  anterior 
extremity  of  the  posterior  horn  is  continuous,  inferiorly,  with 
the  beginning  of  the  inferior  horn.  At  the  junction  of  the  two 
is  a  triangular  area,  the  trigonum  collaterale. 

The  inferior  horn  (cornu  inferius,  Figs.  39,  45,  49,  and  53) 


124  THE    CEREBRUM 

is  the  ventricle  of  the  temporal  lobe.  Its  course  is  crescentic, 
as  it  follows  the  perimeter  of  the  internal  capsule.  It  first  runs 
outward  and  backward  from  the  body  of  the  ventricle,  then  it 
turns  downward,  and  finally  it  proceeds  horizontally  forward 
and  inward  to  within  an  inch  of  the  pole  of  the  temporal  lobe. 
In  horizontal  section  just  below  the  general  cavity  of  the 
ventricle,  the  inferior  horn  is  triangular.  In  that  position  it 
has  a  posterior  wall  (or  floor  in  the  horizontal  part),  a  medial 
wall,  and  a  curved  antero-lateral  wall  (or  roof  in  the  horizontal 
portion)  which  is  continuous  above  with  the  outer  wall  and 
floor  of  the  central  part  of  the  ventricle. 

The  parts  found  in  the  walls  of  the  inferior  horn  may  be 
enumerated  as  follows: 

Roof  (or  antero-lateral  wall) — 

Inferior  lamina  of  internal  capsule,  partially  covered  by 
tapetum,  tail  of  caudate  nucleus,  stria  terminalis  and 
amygdala. 
Floor  (or  posterior  wall) — 

Eminentia  collateralis  (trigonum  collaterale), 
Hippocampus, 
Crus  of  fornix. 
Inner  wall  (medial) — 

Epithelium  (of  hemisphere  wall)  covering 
Pulvinar, 
Chorioid  plexus, 
Chorioidal  fissure,  and 
Dentate  fascia. 
The  structures  in  the  roof  of  the  inferior  horn  have  been  suflS- 
ciently  described.     They  are  easily  understood  when  it  is  re- 
called that  the  roof  of  the  horn  is  continuous  with  the  outer  wall 
and  floor  of  the  central  part  of  the  ventricle;  the  tapetum,  the 
internal  capsule  (inferior  lamina),  the  cauda,  amygdala  and  the 
stria  terminalis  form  it. 

Beginning  at  the  trigonum  collaterale  (Figs.  45  and  49)  and 
extending  along  the  outer  border  of  the  floor  to  the  end  of  the 
inferior  horn  there  is  sometimes  a  low  ridge  caused  by  the  collat- 
eral fissure.     It  is  the  eminentia  collateralis,  and  is  present  only 


INFERIOR  HORN   OF  VENTRICLE 


125 


when  the  anterior  part  of  the  collateral  fissure,  as  well  as  the 
middle  part,  is  a  complete  fissure.  The  short  eminence  at  the 
entrance  to  the  inferior  horn,  called  the  trigonum  collaterale,  is 


Fig.  47. — Horizontal  section  of  cerebrum  just  below  splenium  of  corpus 
callosum,  showing  commissura  hippocampi,  fornix,  septum  pellucidum,  the  island 
and  lateral  ventricles.     (Original.) 

S.  C.  A.  Sul.  circularis  anterior.     S.  C.  P.  Sul.  circularis  posterior. 


constant  in  its  presence;  it  is  produced  by  the  middle  division  of 
the  collateral  fissure.  In  front  of  this  eminence  and  medial  to 
it   is   a   prominent   ridge,    the   hippocampus,   which   enlarges 


126  THE    CEREBRUM 

downward  to  a  lobulated  extremity,  the  pes  hippocampi,  divided 
by  shallow  grooves  into  several  digits  (digitationes  hippocampi, 
Fig.  45).  The  ridge  is  due  to  the  large  development  of  olfactory 
cortex  along  the  chorioidal  fissure.  The  hippocampal  sulcus  is 
a  very  superficial  groove  between  the  hippocampal  gyrus  and 
the  dentate  fascia;  it  is  parallel  with  the  hippocampus,  but  it 
has  nothing  to  do  with  its  formation.  The  hippocampus  was 
formerly  considered  an  invagination  due  to  the  hippocampal 
fissure  (G.  Elliot  Smith). 

The  ventricular  surface  of  the  hippocampus  is  formed  by  a 
lamina  of  white  matter,  the  alveus,  but  the  deeper  part  is 
cortical  matter  composed  almost  entirely  of  pyramidal  cell- 
bodies.  The  crus  of  the  fornix  (fimbria  hippocampi)  rests  in  the 
concavity  of  the  hippocampus,  where  most  of  its  fibers  originate, 
though  a  small  bundle  of  them  originates  beyond  it  in  the 
uncus. 

The  chorioid  epithelium  (lamina  chorioidea  epithelialis)  (Figs. 
37,  46  and  85),  representing  the  hemisphere  wall,  forms  the 
floor  of  the  chorioidal  fissure  and  the  whole  medial  wall  of  the 
inferior  horn.  It  covers  the  cushion-like  projection  (the  pul- 
vinar)  of  the  thalamus,  which  forms  a  small  part  of  both  roof  and 
inner  wall.  Behind,  it  is  attached  to  the  crus  of  the  fornix, 
from  which  it  extends  forward  to  the  stria  terminalis.  The 
epithelium  covers  the  chorioidal  fissure  except  at  the  lower  part, 
where  there  is  a  small  cleft  which  forms  a  communication  be- 
tween the  horn  and  the  anterior  subarachnoid  space.  Through 
the  chorioidal  fissure  a  fold  of  pia  mater  projects  toward  the 
ventricle,  and  pushing  the  epithelium  before  it  into  the  horn, 
forms  the  chorioid  plexus  of  the  inferior  horn  (Figs.  46  and  47). 
The  chorioid  plexus  of  the  inferior  horn  is  continuous  with  that 
in  the  body  of  the  ventricle,  both  lying  in  the  chorioidal  fissure. 

In  connection  with  the  medial  wall  of  the  inferior  horn, 
mention  should  be  made  of  the  hippocampal  formation.  It  is  de- 
veloped along  the  convexity  of  the  inferior  part  of  the  chorioidal 
fissure  from  which  it  is  separated  by  the  crus  fornicis  and  its 
filamentous  extension,  the  fimbria  hippocampi.  The  hippo- 
campal formation  comprises  the  dentate  fascia,  the  hippocampus 


THIRD   VENTRICLE  1 27 

and  the  hippocampal  gyrus.  Its  resemblance  to  the  "  sea  horse" 
can  be  seen  only  in  section.  Behind  the  crus  fornicis  and  below 
the  fimbria  lies  the  dentate  fascia,  already  described  (p.  82) 
which  in  frontal  section  constitutes  the  nose  of  the  horse;  the 
hippocampus  forms  the  top  of  the  head  and  the  arched  neck;  the 
hippocampal  gyrus  represents  the  front  of  the  neck  and  chest. 
The  hippocampal  formation  is  like  the  letter  S.  In  man  it 
includes  almost  the  entire  olfactory  cortex  (Fig.  85). 

THE  THIRD  VENTRICLE  AND  INTER-BRAIN 

{V entriculus  Tertius  and  Diencephalon) 

The  inter-brain  (diencephalon)  is  median  in  position  (Figs. 
33 J  34?  35y  37  ^^^  5^)-  It  is  situated  beneath  the  fornix  and 
the  layer  of  epithelium  extending  from  the  border  of  the  fornix 
to  the  stria  terminalis.  The  chorioid  tela  of  the  third  ventricle 
only  intervenes  between  them.  Laterally,  it  is  bounded  by  the 
superior  laminae  of  the  internal  capsules.  The  ventricle  of  the 
inter-brain  is  the  third  in  number.  The  third  ventricle,  there- 
fore, is  located  in  the  median  plane;  and  is  at  a  lower  level  than 
the  ventricles  of  the  hemispheres.  It  is  made  up  of  two  parts 
in  the  adult,  which  embryologically  are  distinct:  the  posterior 
part,  that  lying  between  the  thalami,  is  the  proper  ventricle  of 
the  diencephalon;  the  small  anterior  part,  called  the  aula,  is 
the  median  ventricle  of  the  telencephalon,  with  which  the 
lateral  ventricles  communicate  through  the  interventricular 
foramina.  Posteriorly,  the  third  ventricle  is  joined  to  the 
fourth  ventricle  by  the  cerebral  aqueduct.  It  is  a  narrow, 
vertical  clef  t  about  2.5  cm.  (i  in.)  in  length  from  before  backward 
and  6  mm.  (0.25  in.)  broad  at  its  widest  part.  It  separates  the 
thalami  and  extends  almost  to  the  inferior  surface  of  the 
cerebrum.  The  roof  (Figs.  35,  44,  48,  50  and  54)  follows  the 
curve  of  the  fornix  and  arches  from  the  posterior  commissure 
forward  to  the  anterior  commissure.  There  is  a  little  recess 
above  the  anterior  commissure  and  between  the  columnae  of  the 
fornix,  bounded  in  front  by  the  inferior  angle  of  the  septum  pel- 
lucidum,  called  the  recessus  triangularis,  in  which  the  roof  and 


128 


THE    CEREBRUM 


anterior  wall  meet.  The  anterior  wall  extends  from  the  trian- 
gular recess  down  to  the  optic  recess,  at  the  angle  between  the 
lamina  terminalis  and  the  optic  chiasma.     This  angle  is  so 


Fig.  48. — Horizontal    section    of    cerebrum.     Fornix    turned    back,    showing 
chorioid  tela  of  third  ventricle,  and  internal  cerebral  veins.     (Original.) 


named  because  on  either  side  of  it  there  is  a  lateral  extension  of 
the  third  ventricle  between  the  lamina  terminalis  and  the 
columna  of  the  fornix,  which  is  located  in  the  root  of  the  em- 


FLOOR    OF    THIRD   VENTRICLE  1 29 

bryonic  optic  vesicle.  The  floor  (Fig.  34)  describes  two  arches, 
convex  toward  the  ventricle.  The  first  arch,  very  convex  and 
short,  stretches  between  the  optic  recess  and  the  infundibulum, 
in  which  the  floor  reaches  its  lowest  point.  The  distance  from 
the  infundibulum  to  the  anterior  orifice  of  the  cerebral  aqueduct 
is  spanned  by  the  second  arch.  It  is  long  and  flat.  Its 
posterior  extremity  is  but  1.7  mm.  (0.07  in.)  below  the  pos- 


FiG.  49. — Transverse  section  of  left  cerebral  hemisphere  cutting  the  splenium 
and  showing  the  posterior  horn  and  the  floor  of  the  inferior  horn  of  the  lateral 
ventricle.     {Original.) 

a.  Crus  fornicis.  b.  Fis.  hippocampi,  c.  Hippocampus,  d.  Fascia  dentata.  e. 
Eminentia  coUateralis.  f.  Fis.  collateralis.  h.  Calcar  avis.  i.  Bulb  caused  by  forceps 
major,  j.  Tapetum.  k.  Radiatio  occipito-thalamica.  1.  Fasciculus  longitudinalis  in- 
ferior. 

terior  commissure ;  the  anterior  orifice  of  the  cerebral  aqueduct 
separates  them.  The  ventricle  is  thus  contracted  behind  to  the 
size  of  the  cerebral  aqueduct  with  which  it  is  continuous.  The 
lateral  walls  (Figs.  34  and  37)  are  close  together  throughout. 
At  one  point  near  the  middle  they  come  together  and  are  joined 
by  the  massa  intermedia  (middle  commissure).  Antero- 
superiorly,  the  lateral  wall  is  perforated  by  the  interventricular 
9 


130  THE   CEREBRUM 

foramen  (of  Monro) .     That  foramen  constitutes  the  slight  separa- 
tion between  the  front  of  the  thalamus  and  the  columna  of  the 
fornix.     It  opens  into  the  lateral  ventricle  at  the  junction  of 
the  anterior  horn  with  the  central  part.     The  ependyma  which 
lines  the  third  ventricle  is  continuous  through  the  interven- 
tricular foramen  with  the  lining  of  the  lateral  ventricle.     But 
one  layer  of  the  ependyma  is  present  in  the  roof  of  the  ventricle; 
that  is  the  epithelial  layer.     The  third  ventricle,  like  all  true 
ventricles,  is  occupied  by  cerebrospinal  fluid. 
The  following  are  the  boundaries  of  the  third  ventricle : 
Roof- 
Posterior  commissure  and  commissura  habenularum, 

Roof  epithelium  and  pineal  body, 

Chorioid  tela  and  plexuses. 

Fornix  and  commissura  hippocampi. 
Anterior  wall — 

Epithelium,  covering 

Columnae  of  fornix,  anterior  commissure,  and 
Lamina  terminalis. 
Floor- 
Optic  chiasma, 

Tuber  cinereum  and  infundibulum. 

Corpora  mammillaria, 

Posterior  perforated  substance  (of  mid-brain), 

Tegmenta  (of  mid-brain). 
Posteriorly — 

Ventricle  is  continuous  with  cerebral  aqueduct. 
Lateral  wall — 

Thalamus  and  reflected  hypothalamic  substance, 

Columna  of  the  fornix,  and 

Foramen  interventricular  between  them. 

Roof. — ^A  band  of  white  fibers  passes  across  the  back  part  of 
the  third  ventricle  and  supports  the  posterior  end  of  the  roof 
epithelium.  That  band  is  the  posterior  commissure  {com- 
missura posterior,  Figs.  34  and  50).  It  crosses  immediately 
in  front  of  the  corpora  quadrigemina.  Beneath  it  is  the 
anterior  orifice  of  the  cerebral  aqueduct.     The  pineal  body  is 


PINEAL  BODY  13I 

above  and  behind  it,  and  the  commissure  fuses  with  the  ventral 
pineal  lamina.  The  posterior  commissure  stretches  from  the 
central  gray  substance  of  the  mid-brain  on  one  side,  over  the 
aqueduct,  to  the  gray  substance  of  the  opposite  side  and  also 
contains  decussating  fibers  of  the  medial  longitudinal  bundle 
(Heald).     The  commissure  is  in  need  of  further  investigation. 

The  roof  epithelium  (Figs.  48  and  54)  of  the  third  ventricle 
stretches  from  the  posterior  commissure  to  the  anterior  com- 
missure and  laterally  is  attached  to  the  upper  medial  border  of 
the  thalamus.  It  is  the  superficial  layer  of  the  ependyma;  but 
it  is  here  the  only  adult  representative  of  the  roof  of  the 
diencephalon.  The  roof  epithelium  presents  two  longitudinal 
folds  suspended  in  the  ventricle.  The  lower  layer  of  the 
chorioid  tela  of  the  third  ventricle  invests  the  roof  epithelium 
superiorly;  and,  dipping  down  into  the  longitudinal  folds, 
that  inferior  layer  forms  the  chorioid  plexuses  of  the  third 
ventricle.  At  the  back  part  in  the  middle  line  there  is  a  pouch- 
like evagination  of  the  roof  of  the  diencephalon  in  the  embryo 
which  develops  into  the  pineal  body;  and  there  remains  a  slight 
pit  called  the  pineal  recess  in  the  adult  condition.  A  second 
evagination  occurs  just  above  the  pineal  recess  which  forms  the 
epipineal  recess.  The  epipineal  evagination  probably  represents 
the  anterior  pineal  body  of  reptiles. 

Pineal  Body  {Corpus  pineale,  Figs.  50,  55  and  loi). — It  is  a 
cone-shaped  body,  6  mm.  (0.25  in.)  high  and  4  mm.  (0.17  in.) 
in  diameter,  joined  to  the  roof  of  the  third  ventricle  by  a 
flattened  stalk,  the  habenula.  It  is  also  called  the  epiphysis. 
The  pineal  body  is  situated  in  the  floor  of  the  transverse  fissure 
of  the  cerebrum,  directly  below  the  splenium  of  the  corpus 
callosum  and  rests  between  the  superior  coUiculi  of  the  quadri- 
geminal  bodies  on  the  posterior  surface  of  the  mid-brain.  It  is 
closely  invested  by  pia  mater.  The  habenula  splits  into  a  dorsal 
and  a  ventral  lamina,  which  are  separated  by  the  pineal  recess. 
The  ventral  lamina  fuses  with  the  posterior  commissure;  but  the 
dorsal  stretches  forward  over  the  commissure  in  continuity  with 
the  roof  epithelium.  The  border  of  the  dorsal  lamina  is  thick- 
ened along  the  line  of  attachment  to  the  thalamus  and  forms  the 


132  THE    CEREBRUM 

stria  medullaris  thalami  (pineal  stria).  The  thickening  is  due 
to  the  presence  of  a  bundle  of  fibers  derived  from  the  columna 
of  the  fornix  and  the  intermediate  stria  of  the  olfactory  tract. 
Between  the  medullary  striae  at  the  posterior  end  there  is  a 
transverse  band  the  commissura  hahenularum,  through  which 
the  fibers  of  the  striae  partially  decussate  to  the  nucleus  ha- 
benulae  in  the  thalamus. 

The  interior  of  the  pineal  body  is  made  up  of  closed  follicles 
surrounded  by  ingrowths  of  connective  tissue.  The  follicles  are 
filled  with  epithelial  cells  mixed  with  calcareous  matter,  the 
brain-sand  (acervulus  cerebri).  Calcareous  deposits  are  found 
also  on  the  pineal  stalk  and  along  the  chorioid  plexuses.  The 
function  of  the  pineal  body  is  unknown.  Des  Cartes  face- 
tiously suggests  that  it  is  the  abode  of  the  spirit  (the  sand)  of 
man.  In  reptiles  there  are  two  pineal  bodies,  an  anterior  and  a 
posterior,  of  which  the  posterior  remains  undeveloped  but  the 
anterior  forms  a  rudimentary,  cyclopean  eye.  In  the  Hatteria, 
a  New  Zealand  lizard,  it  projects  through  the  parietal  foramen 
and  presents  an  imperfect  lens  and  retina  and,  in  its  long  stalk, 
nerve  fibers.  The  human  pineal  body  is  probably  homologous 
with  the  posterior  pineal  body  of  reptiles. 

The  chorioid  tela  of  the  third  ventricle  (velum  interpositum. 
Figs.  48,  50  and  54)  is  the  triangular  fold  of  pia  mater  spread 
over  the  dorsum  of  the  inter-brain.  It  lies  underneath  the  for- 
nix and  the  chorioid  epitheHal  lamina  which  stretches  from  the 
body  of  the  fornix  lateralward  to  the  stria  terminalis.  Its  apex 
is  just  behind  the  anterior  commissure,  and  its  base,  directed 
backward,  is  continuous,  by  the  upper  layer,  with  the  pia  mater 
of  the  occipital  lobes;  and,  by  the  inferior  layer,  it  is  continuous 
with  the  pia  on  the  posterior  surface  of  the  mid-brain  and 
cerebellum.  Each  border  constitutes  the  chorioid  plexus  of  the 
lateral  ventricle  and  is  seen  (through  the  epithelium)  in  the  floor 
of  its  central  part.  The  median  part  of  the  inferior  lamina  of 
the  chorioid  tela  invests  the  roof  epithelium  of  the  third 
ventricle  and  the  lateral  portion  covers  the  medial  half  of  the 
upper  surface  of  each  thalamus.  This  layer  forms  the  two 
chorioid  plexuses  of  the  third  ventricle  which  depend  from  its 


ANTERIOR    WALL  I33 

median  portion.  Between  the  inferior  and  superior  laminae  is 
enclosed  some  connective  tissue  through  which  the  internal 
cerebral  veins  run  backward  to  the  base  of  the  tela;  there  they 
unite  and  form  the  great  cerebral  vein  (Galeni). 

Anterior  Wall. — The  anterior  commissure  {commissura  an- 
terior cerebri,  Figs.  35,  50  and  96)  is  a  very  distinct  round 
bundle  of  white  fibers  about  3  mm.  (.12  in.)in  diameter.  It  is 
seen  in  the  anterior  wall  of  the  third  ventricle  supporting  the 
roof  epithelium.  The  epithelium  there  bends  down  between 
the  columnae  of  the  fornix  and  invests  the  ventricular  surface 
of  the  commissure.  The  columnae  of  the  fornix  and  the  com- 
missure bound  the  recessus  triangularis,  in  which  the  roof  and 
anterior  wall  of  the  third  ventricle  meet.  The  anterior  com- 
missure rests  upon  the  upper  extremity  of  the  lamina  terminalis, 
between  the  columnae  fornicis,  behind,  and  the  lamina  rostralis 
of  the  corpus  callosum,  in  front.  With  the  last  two  structures 
it  is  developed  in  the  lamina  terminalis.  It  is  the  most  impor- 
tant connecting  link  between  the  hemispheres  in  vertebrates 
without  a  corpus  callosum  (all  below  mammals).  Bending 
sharply  backward  in  the  cerebral  hemisphere  the  anterior 
commissure  pierces  the  inferior  part  of  the  globus  pallidus  and 
then  radiates  toward  the  cortex,  some  of  its  fibers  entering 
the  external  capsule.  It  contains  two  groups  of  fibers:  (i) 
The  anterior  group,  which  is  the  commissure  of  the  rhinen- 
cephalon,  called  the  pars  olfactoria;  and  (2)  the  posterior  group, 
the  pars  occipito-temporalis.  The  pars  olfactoria  probably 
contains  two  fasciculi:  {a)  A  commissural  bundle  which  rises 
in  the  cortex  of  the  olfactory  tract,  ascends  vertically  to  the 
commissure,  traverses  it  and  bends  sharply  downward  to  the 
opposite  tract;  then  its  fibers  run  forward  to  the  olfactory  bulb 
and  terminate  in  the  granular  and  glomerular  layers,  {b) 
A  projection  bundle  which  rises  in  the  anterior  perforated 
substance  and  septum  pellucidum.  Ascending  to  the  com- 
missure it  bifurcates  into  a  direct  and  a  crossed  fasciculus. 
The  direct  fasciculus  joins  the  crossed  fasciculus  from  the 
opposite  side,  forming  the  stria  terminalis  whose  course  has 
already  been  traced  to  the  nucleus  amygdalae.     This  is  the 


134 


THE   CEREBRUM 


fasciculus  olfacto-amygdalaris.  The  pars  occipito-temporalis 
connects  the  tentorial  areas  and  the  hippocampal  formations 
of  the  two  hemispheres  together,  regions  which  are  not  con- 


FiG,  50. — Horizontal  section  of  cerebrum  through  genu  and  below  splenium 
of  corpus  callosum.  Fornix  and  chorioid  tela  turned  back  to  show  inter-brain 
and  third  ventricle.     {Original.) 

a.  Head  of  caudate  nucleus,  b.  Stria  meduUaris  thalami  (or  pineal  stria.)  e.  Chorioid 
groove,  d.  Trigonum  habenulae.  e.  Pineal  body.  f.  Tail  of  caudate  nucleus.  g. 
Tapetum.  h.  Occipito-thalamic  radiation,  i.  Inferior  longitudinal  fasciculus,  j.  An- 
terior horn  of  lateral  ventricle,  k.  Columna  of  fornix.  1.  Recessus  triangularis,  m. 
Anterior  commissure,  n.  Massa  intermedia  (or  middle  commissure),  o.  Posterior  com- 
missure,    p.  Superior  quadrigeminal  coUiculus.     q.  Posterior  horn  of  lateral  ventricle. 


nected  by  the  corpus  callosum.  In  man  it  is  larger  than  the 
pars  olfactoria.  It  bends  horizontally  backward  under  the 
head  of  the  caudate  nucleus  and  runs  longitudinally  through 
the  inferior  part  of  the  globus  pallidus.     Backward   to  the 


PINEAL  BODY  I35 

frontal  plane  cutting  the  mammillary  bodies  it  is  clearly  visible 
to  the  naked  eye;  then  it  radiates  to  the  temporo-occipital 
and  to  the  hippocampal  cortex.  A  thin  transverse  sheet  of 
gray  matter,  called  the  lamina  terminalis,  extends  downward 
and  forward  from  the  anterior  commissure  to  the  optic  chiasma 
and  completes  the  anterior  wall  of  the  ventricle  (Figs.  17, 
34  and  96).  Between  the  chiasma  and  the  lamina  terminalis 
is  a  sharp  angle  which  terminates  on  either  side  in  a  small  pit, 
called  the  optic  recess. 

The  floor  of  the  third  ventricle  is  very  narrow  (Figs.  21  and 
37).     It  is  formed  by  the  interpeduncular  structures  plus  the 

Olfactory  bulb 

Medial  olfactory  stria 
Subcallosal  gyrus 

Column  (anterior  pillar)  ^^ 

Digitations  (pes)  of  the 
hippocampus 

~"        M  Gi     I  /w\l  MB  \[/§\  \     @\ Amygdaloid  nucleus 

Mammillo-thalamic   fasciculus. 

Stria  terminalis  of  thalamus-  ---1---™ 

^    .  ,   ,.     .      ,   ,    ,  -Jl" WUSSB^  II/I  —  -  Hippocampus  major 

Stria  medullans  of  thalamus  — *-^«"™  """™  ' ■"  ""' 

Crus  (posterior  pillar) 

Epiphysis  (below)  

Hippocampal  (commissure  lyra) 
Fig.  51. — Dorsal  view  of  fornix.      {Morris.) 

tegmenta,  namely:  optic  chiasma,  tuber  cinereum  and  in- 
fundibulum,  corpora  mammillaria,  posterior  perforated  sub- 
stance and  the  tegmenta.  The  last  two  are  portions  of  the 
mid-brain;  the  others  belong  to  the  fore-brain  with  the  surface 
of  which  we  have  already  studied  them,  and  all  extend  laterally 
beneath  the  thalami. 

The  third  ventricle  has  its  lateral  wall  formed  chiefly  by  the 
thalamus  and  the  columna  of  the  fornix  (Figs.  33  and  44). 
Below  a  slight  longitudinal  groove,  extending  from  the  optic 
recess  to  the  cerebral  aqueduct  and  called  the  sulcus  hypo- 
thalamicus,  the  thalamus  is  covered  by  upturned  hypothalamic 


136 


THE    CEREBRUM 


gray  matter  and  by  the  upper  part  of  the  central  gray  sub^ 
stance  of  the  mid-brain.  The  thalamus  forms  the  immediate 
lateral  wall  above  this  hypothalamic  groove.  The  sulcus 
hypothalamicus  is  beheved  to  represent  the  sulcus  limitans 
separating  the  ventral  and  dorsal  laminae  of  the  embryo.  This 
places  the  origin  of  the  thalamus  in  the  dorsal  lamina  (the 
afferent  lamina). 

The  columna  of  the  fornix  diverging  from  its  fellow  proceeds 
downward  and  backward  to  the  corpus  mammillare  through 


Fornix 
Anterior  commissure        . 


Perforating  fibers 


Medullary  stria  of  thalamus 


Subcallosal  gyrus 


Parolfactory   area  ^ 


Gyrus  rectus  ^ 


Olfactory  tract 
Olfactory  bulb 


Gyrus  cinguli 
,Cingulum 

Longitudinal  striae 
^«'*"on  corpus  callosum 

Hippocampal  commis- 
sure (Lyre) 

Anterior  thalamic 
nucleus 

Habenular  nucleus 


."■ '  Habenulo-peduncular 
tract  (fasciculus  ret- 
rofiexus) 


'  ^»  Mammillo-mesenceph- 
\  alic  fasciculus 

--^x  Pedunculo-tegmental  tract 
Interpeduncular  nucleus 


Uncus 


Fimbria  hippocampi 
Mammillary  body 
Anterior  perforated  substance 


Olfactory 
fasciculus 


Fig.  52. — Lateral  view  of  fornix.       {Morris.) 


the  medial  part  of  the  thalamus.  In  the  ventricle,  the  pars 
libera  of  the  columna  fornicis  is  covered  by  the  ependymal 
epithelium.  It  bounds  the  interventricular  foramen  in  front. 
Thalamus  (Thalamus — a  bed,  Figs.  50,  54,  55  and  56). — 
It  is  the  great  ganglion  of  the  inter-brain.  The  thalamus  is  an 
important  sensory  relay  station.  Its  medial  part  is  concerned 
with  smell  (E.  Sachs)  and  its  lateral  part  with  common  sensa- 
tion and  taste.  According  to  Head  and  Holmes,  it  is  also  an 
organ  of  consciousness  for  impulses  of  pain  and  temperature. 
The  third  ventricle  separates   the  thalami  from  each  other, 


SURFACES    OF   THALAMUS 

except  at  the  mid-point  where  they  are  joined  by  the  massa 
intermedia.  The  thalamus  is  situated  behind  and  medial  to 
the  corpus  striatum,  and  projects  backward  over  the  mid- 
brain. Laterally,  it  rests  against  the  superior  lamina  of  the 
internal  capsule,  which  separates  it  from  the  lentiform  nucleus. 
The  thalamus  is  shaped  like  an  egg,  with  the  small  end  directed 
forward.  It  measures  4  cm.  or  about  one  and  a  half  inches  in 
length  and  2.5  cm.  or  one  inch  in  width  and  thickness.  It  has 
an  anterior  and  a  posterior  extremity  and  four  surfaces: 
Superior,  inferior,  medial  and  lateral. 

Extremities. — The  anterior  extremity  of  the  thalamus  is  lost 
in  a  large  group  of  fibers  (frontal  stalk)  which  runs  through  the 
frontal  part  of  the  internal  capsule.  The  free  posterior  end 
(Fig.  56)  presents  a  large  pillow-like  prominence  the  pulvinar 
and  beneath  it  are  two  smaller  swellings;  the  outer  one  which 
forms  the  lowest  point  of  the  thalamus  is  the  lateral  geniculate 
body;  the  medial  geniculate  body  is  the  other.  The  two  geniculate 
bodies  constitute  the  metathalamus  (Fig.  55). 

Surfaces. — The  lateral  and  inferior  surfaces  of  the  thalamus 
are  attached  so  that  they  can  be  seen  only  in  section;  but 
the  medial  and  superior  surfaces  are  almost  entirely  free. 
A  thin  layer  of  meduUated  fibers  called  the  stratum  zonale 
forms  the  free  surfaces.  The  medial  surface  of  the  thalamus 
forms  the  immediate  lateral  wall  of  the  third  ventricle  as  far 
down  as  the  sulcus  hypothalamicus  (Fig.  34).  It  is  joined  to 
the  medial  surface  of  the  opposite  thalamus  by  the  massa 
intermedia.  It  is  bounded  above  by  the  medullary  stria.  The 
superior  surface  of  the  thalamus  is  divided  by  an  oblique 
groove,  the  chorioidal  groove^  lying  just  medial  to  the  taenia 
chorioidea,  into  two  areas — a  medial  and  lateral  (Fig.  56). 
The  medial  area  is  covered  by  the  chorioid  tela  of  the  third 
ventricle  and  the  fornix.  Medially,  it  is  bounded  by  the  medul- 
lary stria  of  the  thalamus.  Posteriorly  next  the  stria  is  a  tri- 
angular depression  bounded  behind  by  a  transverse  groove  in 
front  of  the  corpora  quadrigemina  and  by  a  slight  groove,  the 
sulcus  habenulae,  laterally.  That  depressed  surface  is  called 
the  triangle  of  the  hahenula  (trigonum  habenulae).     Beneath  the 


138 


THE    CEREBRUM 


triangle  is  one  of  the  thalamic  nuclei,  the  nucleus  habenulcd. 
The  lateral  area  of  the  superior  surface  covered  by  the  lamina 


PitftAL  Recess 


Fig.  S2)- — ^Lateral  and  dorsal  view  of  the  ventricles.    Diagrammatic.    {Original.) 
A.  Lateral  view  of  the  ventricles.    B.   Dorsal  view  of  the  ventricles. 

afl&xa  is  seen  in  the  floor  of  the  lateral  ventricle.  It  presents 
an  anterior  elevation,  the  anterior  tubercle  (tuberculum  anterius 
thalami),  beneath  which  is  the  anterior  nucleus  of  the  thalamus. 


TEGMENTAL  PART   OF  HYPOTHALAMUS  1 39 

The  lamina  afiixa  of  the  chorioid  epithelial  lamina  which 
covers  this  outer  area  separates  it  from  the  ventricular  cavity. 
A  lamina  of  fibers,  the  external  medullary  lamina,  forms  the 
lateral  surface  of  the  thalamus  and  rests  upon  the  superior 
lamina  of  the  internal  capsule.  Its  fibers  are  continuous 
with  those  of  the.  capsule.  The  inferior  surface  blends  with 
the  superior  surface  of  the  tegmentum  and  substantia  nigra, 
and  forms  the  laminae  and  nuclei  of  the  tegmental  part  of  hypo- 
thalamus (see  below). 

Tegmental  Hypothalamic  Region  (Figs.  37  and  54). — The 
hypothalamus  is  divided  into  three  parts,  viz.,  the  optic ^  the 
mammillary  and  the  tegmental.  The  optic  and  the  mammillary 
parts  have  been  considered  with  the  base  of  the  fore-brain;  the 
tegmental  part  is  visible  only  in  sections.  The  pars  tegmentalis 
hypothalami  is  composed  of  three  layers:  (i)  Stratum  dorsale 
next  the  thalamus;  (2)  zona  incerta,  the  middle;  and  (3) 
hypothalamic  nucleus,  the  inferior.  The  nucleus  hypo- 
thalamicus  (Luysi)  is  ventro-lateral  in  position  and  Hes  be- 
tween the  base  of  the  internal  capsule  and  the  zona  incerta. 
It  has  the  shape  of  a  flattened  cyHnder  10  mm.  by  3  mm.  and 
about  I  mm.  in  thickness.  Like  the  substantia  nigra  just  be- 
low it,  it  is  composed  of  pigmented  gray  matter.  The  reticular 
formation  of  the  tegmentum  continuing  beneath  the  thalamus 
forms  the  zona  incerta.  The  stratimi  dorsale  is  made  up  as 
follows:  (a)  Fibers  from  the  medial  longitudinal  bundle 
(Meynert);  {b)  the  brachium  conjunctivum  (Forel),  in  which  is 
the  upper  end  of  the  red  nucleus  of  the  tegmentum;  (c)  the 
medial  fillet,  which  runs  lateral  and  sUghtly  ventral  to  the  red 
nucleus;  (d)  the  rubro- thalamic  tract;  (e)  the  strio-fugal  tracts. 

The  red  nucleus  {nucleus  ruber,  Fig.  44)  is  an  elongated  ovoid 
mass  of  slightly  pigmented  neurone  bodies,  located  near  the  me- 
dian plane  in  the  tegmental  part  of  the  hypothalamus.  It 
measures  about  10  mm.  in  length  and  3  mm.  in  width  and  is  al- 
most round  in  cross  section.  Its  anterior  end  is  just  behind  the 
mammillary  bodies  and  its  posterior  end  touches  the  transverse 
plane  between  the  superior  and  inferior  quadrigeminal  bodies. 
It  lies  at  the  same  horizontal  level  as  the  hypothalamic  nucleus, 


I40  THE    CEREBRUM 

but  it  is  somewhat  caudal  to  it:  the  two  nuclei  are  of  the  same 
length  and  the  red  extends  farther  downward  in  the  mid-brain 
and  the  hypothalamic  farther  forward  in  the  inter-brain.  The 
red  nucleus  is  intermediate  between  the  cerebellum  and  the 
thalamus  and  between  the  cerebellum  and  the  spinal  cord. 
It  also  receives  axones  from  the  cerebral  cortex  and  the  globus 
pallidus. 

The  lateral  geniculate  body  {corpus  geniculatum  laterale, 
Fig.  55)  forms  a  slight  swelhng  at  the  lowest  point  of  the 
thalamus.  It  marks  the  apparent  end  of  the  lateral  root  of 
the  optic  tract  and  is  the  terminal  nucleus  of  80  per  cent, 
of  its  fibers.  It  is  joined  to  the  superior  quadrigeminal  emi- 
nence by  the  brachium  superius.  In  appearance  it  is  dark 
colored  and  laminated;  its  gray  matter,  which  contains  pig- 
mented multipolar  cell-bodies,  is  divided  into  thick  layers  by 
thin  laminae  of  fibers  from  the  optic  tract  and  radiation.  The 
processes  of  the  multipolar  cell-bodies  help  to  form  the  optic 
radiation. 

The  medial  geniculate  body  [corpus  geniculatum  mediale), 
also  belongs  to  the  inter-brain  and,  together  with  the  lateral 
geniculate  body,  constitutes  the  metathalamus  (Fig.  55).  It  is 
placed  at  the  end  of  the  medial  root,  as  the  lateral  geniculate  is 
at  the  end  of  the  outer  root,  of  the  optic  tract.  It  rises  up  from 
the  groove  between  the  thalamus  and  corpora  quadrigemina, 
and  is  joined  to  the  inferior  quadrigeminal  eminence  by  the 
brachium  inferius.  The  brachium  superius  sweeps  around  it  in 
front.  The  medial  geniculate  body  is  gray  in  color  and  is  not 
laminated.  Its  cell-bodies  are  small  and  fusiform  in  shape. 
They  perhaps  give  origin  to  the  intercerebral  fibers  (Guddeni) 
of  the  optic  tract  and  to  a  large  part  of  the  acustic  radiation. 

CEREBRUM 

SECTION  II.     THE  MID-BRAIN 
(MESENCEPHALON) 

The  third  division  of  the  cerebrum  is  the  mid-brain  (Figs.  56 
and  57).     It  is  situated  below  and  behind  the  inter-brain  and 


SURFACES    OF    MID-BRAIN  141 

forms  the  connecting  link  between  the  fore-brain  and  the  hind- 
brain.  This  has  suggested  the  name  "isthmus,"  sometimes 
appHed  to  it:  though  isthmus  rhombencephali  refers  only  to  the 
constriction  below  the  corpora  quadrigemina.  The  mid-brain 
is  developed  from  the  middle  of  the  brain-vesicles,  the  mesen- 
cephalon (Figs.  16,  17  and  i8).  The  cavity  of  the  mesenceph- 
alon persists  as  the  cerebral  aqueduct,  which  is  reduced  to  a 
slender  canal  by  the  thickening  of  its  walls,  roof  and  floor,  due 
largely  to  the  ingrowth  of  fibers  from  other  parts  of  the  brain. 
The  cerebral  hemispheres  almost  conceal  the  mid-brain  from 
view;  they  overhang  it  dorsally,  and  the  temporal  lobes,  in- 
closing it  between  them,  bend  medially  and  cover  part  of  its 
anterior  surface.  Only  the  median  part  of  the  anterior  surface 
is  visible  in  the  complete  brain  (Fig.  21).  The  form  of  the  mid- 
brain resembles  a  flattened  cylinder.  Its  axis,  13  mm.  (0.5  in.) 
long,  is  pointed  upward  and  forward,  and  its  long  diameter, 
which  varies  from  2.5  cm.-3.7  cm.  (1-1.5  in.)  in  length,  is 
directed  transversely. 

SURFACES 

The  mid-brain  has  four  surfaces,  viz.,  the  anterior  and  pos- 
terior, which  are  free,  and  the  superior  and  inferior,  representing 
the  ends  of  the  cylinder,  which  are  attached.  The  two  latter 
are  nearly  parallel  with  each  other  and  are  formed  by  section. 

The  superior  surface,  sloping  downward  and  forward,  meets 
the  anterior  surface  at  an  acute  angle.  Its  inclination  is  that  of 
the  posterior  end  of  the  floor  of  the  third  ventricle.  Lateral  to 
the  floor  of  the  ventricle  it  is  attached  to  the  thalami  and  in- 
ternal capsules.  The  blending  of  it  with  the  thalami  forms  the 
structures  of  the  tegmental  hypothalamic  regions  and  the  con- 
tinuations of  the  extreme  lateral  portions,  the  bases  pedunculi, 
enter  into  the  internal  capsules  of  the  hemispheres.  In  the 
median  line  behind  the  third  ventricle  it  is  attached  to  the 
posterior  commissure.  The  superior  surface  is  3.7  cm.  (1.5  in.) 
broad. 

The  inferior  surface  joins  the  upper  surface  of  the  pons.  It 
is  a  little  narrower  than  the  superior  surface.     It  is  about 


142 


THE   CEREBRUM 


3  cm.  (1.25  in.)  broad  and  measures   2.5  cm.   (i  in.)  dorso- 
ventrally. 

The  anterior  surface  (ventral)  of  the  mid-brain  looks  forward 
and  downward  (Figs.  57,  59  and  60).  It  is  deeply  grooved 
longitudinally  by  a  median  sulcus,  the  fossa  inter peduncularis, 
and  is  slightly  concave  from  above  downward.  It  is  separated 
on  either  side  from  the  posterior  surface  by  the  sulcus  lateralis 


Fig.  54. — Transverse  section  of  brain,  cutting  corpora  mammillaria 
(After  Toldt,  Morrises  Anatomy.) 

a.  Lateral  ventricle  (central  portion),  b.  Chorioid  plexus  of  lateral  ventricle,  c.  fCau- 
date  nuclues.  d.  Massa  intermedia,  e.  Internal  capsule.  Lenticular  nucleus,  f.  Puta- 
men;  gh.  Zones,  globus  pallidus.  i.  External  capsule,  j.  Claustrum.  k.  Ansa  pendun- 
cularis.  L  Optic  tract,  m.  Inferior  peduncle  of  thalamus,  n.  Inferior  cornu  of  lateral 
ventricle,  o.  Hippocampus,  p.  Digitations.  q.  Oculomotor  nerve,  r.  Corpus  callosum. 
s.  Fornix,  t.  Third  ventricle,  u.  Thalamus,  v.  Thalamo-mammillary  fasciculus,  w. 
Ansa  lenticularis.  x.  Hypothalamic  nucleus  (corpus  Luysi).  y.  Substantia  nigra,  z. 
Basis  of  cerebral  peduncle,  aa.  Corpus  mammillare.  bb.  Interpeduncular  fossa,  cc. 
Pons  (varolii). 


mesencephali.  Though  partially  concealed  by  the  temporal 
lobes  of  the  cerebrum,  the  anterior  surface  is  unattached.  It 
is  formed  by  a  prominent  band,  the  basis  pedunculi  at  either 
side ;  and  by  a  median  structure,  the  posterior  perforated  substance, 
which  is  inclosed  between  the  two  bases.  The  posterior  per- 
forated substance  forms  the  floor  of  the  median  sulcus.  The 
inner  border  of  the  basis  pedunculi  is  free  and  overhangs  the 


POSTERIOR   SURFACE   OF   MID-BRAIN  1 43 

perforated  substance  slightly.  Thus  is  formed  the  oculomotor 
groove  {sulcus  nervi  oculomotorii)  between  the  basis  and  per- 
forated substance  whence  the  third  cerebral  nerve  emerges 
from  the  brain.  The  fourth  nerve  courses  forward  over  the 
anterior  surface,  but  is  not  attached  to  it. 

The  posterior  surface  (dorsal)  of  the  mid-brain  (Fig.  56), 
though  free,  is  entirely  concealed  by  the  cerebellar  and  cerebral 
hemispheres.  It  forms  part  of  the  floor  of  the  transverse  fissure 
of  the  cerebrum  and  is  covered  by  pia  mater.  The  lateral  sulcus 
bounds  it  on  each  side.  From  the  sulcus  lateralis  it  elevates 
abruptly  toward  the  median  line,  where  it  presents  a  longi- 
tudinal groove.  This  produces  two  ridges  which  are  sub- 
divided by  a  transverse  groove  into  the  four  eminences,  the 
colliculi  of  the  corpora  quadrigemina.  On  either  side,  anterior 
and  a  little  lateral  to  the  quadrigeminal  bodies,  is  the  medial 
geniculate  body,  joined  to  the  inferior  quadrigeminal  coUiculus 
by  an  oblique  ridge,  called  the  brachium  inferius.  The  nearly 
parallel  longitudinal  ridges  below  the  corpora  quadrigemina  are 
formed  by  the  brachia  conjunctiva  of  the  cerebellum.  The  bottom 
of  the  groove  between  them  is  formed  by  the  superior  medullary 
velum  (of  Vieussens) ,  whence  the  trochlear  nerve  (fourth)  is  seen 
issuing. 

I.  Corpora  quadrigemina  and  brachia. 

{I.  Tegmenta 
2.  Substantia  nigra 
3.  Bases  pedunculi. 


Mid-brain  { 


The  four  colHculi  of  the  corpora  quadrigemina  and  the  four 
brachia  connecting  them  with  the  geniculate  bodies  constitute 
the  quadrigeminal  lamina^  which  forms  the  greater  part  of  the 
posterior  surface  of  the  mid-brain  (Fig.  56).  It  is  also  called 
the  tectum.  This  lamina  rests  upon  the  dorsum  of  the  pedun- 
culi cerebri.  The  lamina  quadrigemina  presents  a  small 
median  triangle  between  the  superior  colliculi  and  the  habenula, 
called  the  subpineal  triangle,  in  which  the  pineal  body  rests. 
The  lamina  is  invested  with  pia  mater. 

The  pedunculi  cerebri  are  made  up  of  three  great  divisions,  as 
shown  above;  named  from  before  backward,  they  are:  (i)  The 


144 


THE    CEREBRUM 


bases  pedunculi,  comprising  the  anterior  part;  (2)  the  substantia 
nigra,  which  is  the  middle  part;  and  (3)  the  tegmenta,  which 
are  united  by  a  median  raphe  and  lie  in  the  posterior  region 
next  the  quadrigeminal  lamina.  In  the  median  plane  between 
the  quadrigeminal  lamina  and  the  tegmenta  runs  the  cerebral 
aqueduct. 

The  bases  pedunculi   (Figs.   57,   58,   59  and  60)   are  two 


Fig.  55. — The  region  of  the  mid-brain  showing  pulvinar  of  the  thalamus,  the 
geniculate  bodies,  the  corpora  quadrigemina  and  brachia,  the  pineal  body,  the 
optic  tract  and  the  fourth  nerve.     {Original.) 

a.  Chorioid  groove,  b.  Medial  geniculate  body.  c.  Lateral  geniculate  body.  d.  Medial 
and  lateral  roots  of  optic  tract,  e.  Optic  tract,  f.  Optic  chiasma.  g.  Brachium  inferius. 
h.  Superior  coUiculus  of  corpora  quad.  i.  Pineal  body.  j.  Inferior  colliculus  of  corpory 
quad.  k.  Brach.  superius.  1.  Thalamus,  m.  Fraenulum  veli.  n.  Superior  meduUara 
velum,     o.  Fourth  ventricle,     p.  Trochlear  nerve. 

rounded  bands  of  medullated  fibers,  limited  by  the  inter- 
peduncular fossa  and  lateral  sulcus  of  the  mid-brain.  Each 
basis  pedunculi  is  13  mm.  broad  and  is  distinctly  striated 
longitudinally.  It  issues  from  the  under  surface  of  the  fore- 
brain  at  the  junction  of  the  hemisphere  with  the  thalamus  and, 
trending  toward  the  median  line,  descends  to  the  pons.  At  its 
supperior  end  it  is  continuous  with  the  efferent  tracts  of  the 
internal    capsule.     Four    efferent    tracts    make    up  the  basis 


DORSAL   SURFACE   OF  BRAIN-STEM 


145 


Fig.  56. — The  dorsal  or  posterior  aspect  of  the  inter-brain,  the  mid-brain,  the 
pons  and  the  medulla.  (Original.) 
a.  Anterior  tubercle  of  thalamus,  b.  Pulvinar  of  thalamus,  c.  Brachium  inferius.  d. 
Inferior  coUiculus  of  corpora  quad.  e.  Brachium  conjunctivum.  f .  Corpus  restiforme.  g. 
Brachium  pontis.  h.  Tuberculum  acusticum.  i.  Calamus  scriptorius.  j.  Area  acustica. 
k.  Posterior  median  fissure.  1.  Stalk  of  pineal  body.  m.  Collicvilus  superior  of  corpora 
quad.  n.  Medial  geniculate  body.  o.  Superior  medullary  velum,  p.  Median  groove,  q. 
CoUiculus  facialis,  r.  Fovea  superior,  s.  Medullary  striae,  t.  Trigonum  n.  hypoglossi. 
u.  Fovea  inferior,  v.  Ala  cinerea.  w.  Taenia  ventriculi  quarti.  x.  Posterior  lateral 
sulcus. 


146  THE    CEREBRUM 

pedunculi,    viz.,    the   intermediate,    the    temporo-pontal,    the 
pyramidal,  and  the  fronto-pontal. 

The  deep  portion  of  each  basis  pedunculi  (Fig.  59)  is  occupied 
by  the  intermediate  path  which  rises  in  the  corpus  striatum, 
is  relayed  in  substantia  nigra  and  terminates  in  the  nucleus 
pontis  (Flechsig).  The  intermediate  path  is  made  up  of  two 
tracts,  the  strio-nigral  and  the  nigro-pontal  tract.  The  super- 
ficial part  of  the  basis  is  made  up  of  three  tracts. 

1.  The  lateral  fifth  of  each  basis  contains  the  temporo- 
pontal  tract  (tractus  temporo-pontalis) .  It  is  composed  of 
neurones  which  reach  from  the  temporal  lobe  to  the  pons. 
The  temporo-pontal  tract  rises  in  the  superior,  middle  and 
inferior  temporal  gyri  (Dejerine)  and,  perhaps,  in  parts  of  the 
occipital  lobe  (Zacher)  and  the  parietal  lobe  (Sioli) ;  it  terminates 
chiefly  in  the  nucleus  of  the  pons,  a  few  fibers  going  to  the  motor 
nuclei  of  cranial  nerves  (Spitzka).  The  temporo-pontal  tract 
is  an  efferent  one,  but  is  not  voluntary  motor.  Its  fibers  are 
medullated  later  than  the  pyramidal  tract  (Flechsig). 

2.  The  middle  three-fifths  of  the  basis  pedunculi  (Figs.  59 
and  60)  is  occupied  by  the  pyramidal  tract  {fasciculus  cerebro- 
spinalis) .  Its  fibers  rise  in  the  anterior  central  gyrus  of  the  cere- 
bral cortex;  they  run  through  the  genu  and  anterior  two-thirds 
of  the  occipital  part  of  the  internal  capsule,  form  the  middle 
three-fifths  of  the  basis,  a  part  of  the  basilar  longitudinal  fibers 
of  the  pons,  and  the  pyramid  of  the  medulla.  Below  the 
medulla  they  are  continued  in  the  anterior  and  lateral  pyram- 
idal tracts  of  the  spinal  cord.  Those  fibers  of  the  pyramidal 
tract  which  innervate  the  muscles  of  speech  and  of  the  face  run 
through  the  genu  of  the  internal  capsule  and  constitute  the 
medial  portion  of  the  tract  in  the  mid-brain  and  the  accessory 
lemniscus  (of  Bechterew).  Immediately  behind  the  face  fibers, 
in  the  capsula  interna,  and  lateral  to  them,  in  the  basis  pedunculi, 
are  fibers  which  innervate  the  muscles  of  the  arm.  Still  behind 
these,  in  the  internal  capsule,  and  lateral  to  them,  in  the 
pyramidal  tract  of  the  basis  pedunculi,  are  fibers  for  the  inner- 
vation of  the  trunk  and  leg  muscles. 

3.  The  inner  fifth  of  the  basis  pedunculi  is  composed  of  the 


SUBSTANTIA  NIGRA  147 

fronto-pontal  tract  (tradus  fronto-pontaUs)  (Figs.  59,  63).  The 
origin  of  this  tract  is  in  the  middle  and  posterior  parts  of  the 
three  frontal  gyri.  It  is  meduUated  later  than  the  pyramidal 
tract,  like  the  temporo-pontal  tract.  It  is  an  efferent  tract. 
It  terminates  very  largely  in  the  nucleus  pontis ;  Flechsig  claims 
that  a  few  of  its  fibers  end  in  motor  nuclei  of  cranial  nerves. 
The  fronto-pontal  and  temporo-pontal  tracts  are  probably  con- 
cerned with  some  form  of  coordination  or  inhibition  rather 
than  with  voluntary  motion.  The  intermediate  path  belongs 
to  the  strio-fugal  system  of  fibers  and,  according  to  S.  A.  Kin- 
nier  Wilson,  it  exercises  a  steadying  influence  over  the  lower 
motor  neurones. 

The  Substantia  Nigra  (Figs.  58,  59  and  60) . — The  central  part 
of  the  crura  cerebri  is  a  sheet  of  pigmented  gray  matter.  The 
substantia  nigra  is  visible  at  the  base  of  the  brain  between  the 
bases  pedunculi,  where  it  is  called  the  posterior  perforated 
substance  {substantia  perforata  posterior),  and  its  margin  comes 
to  the  surface  in  each  lateral  sulcus  of  the  mid-brain.  It  extends 
from  the  pons  upward  to  the  corpora  mammillaria  and  nucleus 
hypothalamicus  (Luysi).  Dorsal  to  it  are  the  tegmenta. 
Transversely,  the  substantia  nigra  is  convex  forward,  but  it  is 
slightly  concave  longitudinally.  The  third  nerve  pierces  it  and 
comes  out  through  the  oculomotor  groove.  It  contains  small 
pigmented  multipolar  cell-bodies,  some  of  which  constitute  a 
relay  for  certain  fibers  of  the  medial  fillet  (Barker).  There  is  a 
median  aggregation  of  these  cells  located  just  in  front  of  the 
pons,  the  interpeduncular  nucleus  {ganglion  inter  peduncular  e) . 
According  to  Forel,  this  nucleus  is  connected  by  a  bundle  of 
fibers,  the  fasciculus  habenulo-peduncularis  (fasciculus  re- 
troflexus),  with  the  nucleus  habenulae  of  the  thalamus.  The 
superior  portion  of  the  substantia  nigra  lies  ventral  to  the 
nucleus  hypothalamicus  (Luysi)  on  either  side.  The  nucleus 
hypothalamicus  lies  ventro-lateral  to  the  red  nucleus,  and  is 
separated  from  it  by  the  zona  incerta. 

The  Tegmenta  (Figs.  58,  63  and  64). — The  posterior  divisions 
of  the  pedunculi  cerebri,  which  cover  the  other  divisions,  are  in 
consequence  called  the  tegmenta  {tegmentum — a  cover).     They 


148  THE   CEREBRUM 

are  united  by  a  median  raphe  and  jSit  ventrally  into  the  con- 
cavity of  the  substantia  nigra.     They  are  bounded  by  the 
lateral  sulcus  of  the  mid-brain  on  the  free  side,  where  each 
tegmentum  presents  the  trigonum  lemnisci,  bounded  by  the 
sulcus  lateralis  in    front;    by  the  brachium    inferius    above; 
and  inferiorly  by  the  lateral  fillet.     Dorsally,  the   tegmenta 
fuse  with   the   quadrigeminal  lamina.      Each  tegmentum   at 
the  superior  end  blends  with  the  thalamus,  and  helps  to  form 
the   tegmental   hypothalamic   structures.     Imbedded  in   that 
superior  portion  is  the  red  nucleus  (n.  ruber)  of  the  tegmentum 
(see    tegmental    hypothalamic    region).     Inferiorly,    the    teg- 
menta are  continued  into  the  reticular  formation  of  the  pons. 
The  Cerebral  Aqueduct  {Aqueductus  Cerebri,  Sylvii,  Figs.  17, 
33  and  59). — The  aqueduct  is  a  very  slender  canal  connecting 
the  third  and  fourth  ventricles.     So  it  is  the  ''iter  a  tertia  ad 
quartum   ventriculum."     It   is   situated   in   the   median   line 
near    the   quadrigeminal    lamina.     It    is    13    mm.   long.     In 
shape  it  is  V-like,  above;  elliptical  in  the  middle,  with  a  vertical 
major  axis;    and  T-form,   below,   where  it    joins   the  fourth 
ventricle.     Its  height  varies  between  1.7  mm.  and  3  mm.  (0.07 
and  0.15  in.).    Like  other  ventricles  it  is  lined  with  ependyma. 
A  layer  of  gray  matter,  thickest  on  the  sides  and  floor,  surrounds 
the  aqueduct  of  the  cerebrum.     This  is  the  stratum  griseum 
centrale,  which  gives  rise  to  some  of  the  fibers  of  the  posterior 
commissure.     The    stratum    griseum    centrale    is    continuous 
with  the  gray  matter  of  the  fourth  ventricle.     It  is  composed 
largely  of  gelatinous  gray  substance  and  possesses  few  medullated 
fibers  and  cell-bodies.     The  fibers  constitute  the  system  of  the 
central   gray   substance    called    the   fasciculus    longitudinalis 
dorsalis  (Schiitzi),  which  is  located  in  the  floor  of  the  cerebral 
aqueduct   close    to    the    ependyma.     The  dorsal  longitudinal 
bundle  of  Schiitz  rises  in  the  stratum  griseum  centrale  and  its 
nucleus  tegmenti  dorsalis  of  the  reticular  formation;  it  descends 
through  the  ventricular  gray  substance  of  the  pons  and  the 
medulla  into  the  spinal  cord;  and  it  is  said  to  terminate  in  the 
motor  nuclei  of  cranial  nerves  and  in  other  nuclei.     Its  function 


ANTERIOR   SURFACE   OF  BRAIN-STEM 


149 


Fig.  57. — Anterior  aspect  of  the  mid-brain,  pons  and  medulla.     (Original.) 
a.  Interpeduncular     fossa,     b.  Basis     pedunculi.     c.  Pons.     d.  Trigeminal     nerve,     e. 
Abducent  nerve,     f.  Acustic  nerve,     g.  Facial  nerve,     h.  Intermediate  nerve,     i.  Glosso- 


pharyngeal nerve,  j.  Vagus  nerve,  k.  Accessory  nerve.  1. 
terior  median  fissure,  n.  Optic  tract,  o.  Optic  chiasma.  p. 
fundibulum.  r.  Corpus  mammillare.  s.  Oculomotor  nerve, 
of  optic  tract,  u.  Sulcus  basilaris.  v.  Acustic  nerve. 
d'Azyri).  x.  Pyramid,  y.  Olive,  z.  Anterior  lateral  sulcus. 
bb.  Funiculus  lateralis. 


Hypoglossal  nerve,  m.  An- 
Optic  nerve,  q.  Stalk  of  in- 
t.  Medial  and  lateral  roots 
w.  Foramen  caecum  (Vicq 
aa.  Posterior  lateral  sulcus. 


150  THE    CEREBRUM 

is  in  doubt,  but  it  probably  belongs  to  an  olfactory  reflex 
mechanism. 

In  the  ventral  part  of  the  stratum  griseum  centrale  are 
cell-groups  forming  the  nuclei  of  the  oculomotor  and  trochlear 
nerves;  while  in  the  extreme  lateral  part  of  the  stratum,  the 
mesencephalic  nucleus  of  the  trigeminal  nerve  is  located. 

Nuclei  of  the  Oculomotor  and  Trochlear  Nerves  (Figs.  59  and 
60). — Both  nuclei  together  extend  the  entire  length  of  the 
aqueduct,  and  the  oculomotor  is  prolonged  into  the  wall  of 
the  third  ventricle  where  it  receives  a  bundle  of  fibers  from 
the  opposite  optic  radiation  and  optic  tract.  The  nucleus  of 
the  third  nerve  {n.  oculomotorius) ,  is  a  nucleus  of  origin,  a 
genetic  nucleus.  It  is  composed  of  two  distinct  parts,  a  su- 
perior visceral  part  and  an  inferior  somatic  part.  The  visceral 
part  lies  in  the  lateral  wall  of  the  third  ventricle,  directly 
above  the  mammillary  body.  It  innervates  smooth  muscle 
inside  the  eye.  Lateral  and  dorsal  to  it  lies  the  nucleus  of  the 
posterior  commissure  (nucleus  of  the  medial  longitudinal 
bundle,  nucleus  of  Darkschewitsch).  The  somatic  part  of 
the  oculomotor  nucleus  is  situated  ventral  to  the  superior 
quadrigeminal  colliculus.  It  includes  a  long  lateral  group  of 
cell-bodies  belonging  to  the  nerve  of  the  same  side  and  a 
median  group,  which  contributes  to  both  nerves.  It  supplies 
striated  muscles.  The  two  oculomotor  nuclei  are  associated 
across  the  median  plane  by  decussating  dendrites.  From  them 
the  root  fibers  run  forward  through  the  red  nucleus  and  substan- 
tia nigra  and  issue  from  the  oculomotor  groove.  The  nucleus 
of  the  fourth  nerve  (n.  trochlearis)  is  a  single  oval  mass  of  cell- 
bodies  situated  ventral  to  the  inferior  colliculus  of  the  corpora 
quadrigemina.  This  is  also  a  genetic  nucleus.  The  root  fibers 
of  the  fourth  nerve,  trochlear,  proceed  dorsally  and  caudal  ward 
from  the  nucleus.  They  decussate  with  the  fibers  from  the 
opposite  nucleus  in  the  superior  medullary  velum,  from  which 
they  emerge  on  either  side  of  the  frenulum.  They  then  continue 
in  the  opposite  nerve  around  the  side  and  over  the  anterior 
surface  of  the  mid-brain.     This  is  the  only  nerve  that  decussates 


DORSAL    LONGITUDINAL  BUNDLE   OF   SCHUTZ  151 

en  masse  between  the  genetic  nucleus  and  the  point  of  exit 
from  the  brain. 

The  nucleus  of  the  mesencephalic  root  of  the  trigeminal  nerve 
is  composed  of  large  cell-bodies  scattered  in  the  extreme  lateral 
part  of  the  stratum  griseum  centrale,  from  the  highest  level 
of  the  mid-brain  down  to  the  pons.  There  is  no  break  be- 
tween this  nucleus  and  the  chief  motor  nucleus  of  the  fifth  nerve 
under  the  locus  caeruleus.  The  axones  of  these  large  cell- 
bodies  run  downward  through  the  nucleus,  accumlating  gradu- 
ally until  they  form  a  distinct  crescentic  strand,  which  joins 
the  chief  motor  root  of  the  same  side.  This  is  the  usual  de- 
scription and  it  is  supported  by  Otto  May  and  Sir  Victor 
Horsley;  but  the  studies  of  J.  B.  Johnston  cast  some  doubt 
upon  its  correctness. 

The  opposite  pyramidal  tracts  and  probably  the  three  homo- 
lateral, cerebro-pontal  paths  (fronto-pontal,  temporo-pontal  and 
intermediate  paths)  bring  these  nuclei  into  relation  with  the 
cerebral  cortex;  and  the  anterior  and  the  medial  longitudinal 
bundles  establish  their  reflex  relation. 

Fasciculus  Longitudinalis  Dorsalis  of  Schtitz  (Bechterew's 
dorsal  longitudinal  bundle  of  the  central  gray  substance, 
dorsal  gray  longitudinal  bundle  of  Kolliker).  The  dorsal 
longitudinal  bundle  of  Schutz  rises  in  the  central  gray  sub- 
stance and  its  dorsal  tegmental  nucleus.  In  the  form  of  a  thin, 
broad  tract  it  courses  downward  through  the  gray  substance, 
near  the  ependyma,  as  far  as  the  spinal  cord;  its  fibers  are 
believed  to  terminate  in  the  cranial  nerve  and  other  nuclei. 
The  tract  probably  belongs  to  a  very  primitive  reflex  mechanism 
(olfactory) . 

Formatio  Reticularis  (Fig.  60). — Through  the  greater  por- 
tion of  the  tegmenta  there  are  many  obHque  fibers  interwoven 
with  tracts  of  longitudinal  fibers  so  as  to  produce  a  reticulum  or 
net.  Imbedded  in  the  reticular  formation,  ventro-lateral  to 
the  oculomotor  nucleus,  lies  its  superior  lateral  nucleus,  called 
the  nucleus  tegmenti  profundus.  This  is  the  only  nucleus  in 
the  reticular  formation  of  the  mid -brain.  It  is  composed  of  a 
medial  and  a  lateral  part.    In  the  stratum  griseum  centrale 


152  THE    CEREBRUM 

and  dorsal  to  the  trochlear  nucleus,  the  nucleus  tegmenti 
dorsalis  is  located.  It  extends  a  short  distance  into  the  pons. 
The  reticular  formation  contains  one  large  nucleus  of  pinkish 
color,  the  nucleus  ruber,  which  is  clearly  visible  near  the  median 
raphe  and  the  substantia  nigra;  its  outline  is  definite  because 
it  is  surrounded  by  medullated  fibers.  Many  of  the  oblique 
fibers  of  the  formatio  reticularis  pass  through  the  median 
raphe  into  the  opposite  tegmentum;  they  produce  the  teg- 
mental decussations,  which  are  situated  at  three  successive 
levels,  viz.,  the  superior  colliculus,  the  inferior  coUiculus  and 
the  isthmus  rhombencephali. 

The  tegmental  decussations  at  the  level  of  the  superior  quad- 
rigeminal  colliculus  (the  fountain  decussations)  are:  (i)  The 
dorsal  tegmental  decussation  (Meynerti)  through  which  the 
tecto-spinal  or  anterior  longitudinal  bundle  crosses.  It  is 
situated  between  the  red  nuclei  but  dorsal  to  them.  (2)  The 
middle — the  decussation  of  the  fasciculus  mammillo-tegmentalis. 
(3)  The  ventral  tegmental  decussation  (Foreli)  in  which  the 
tract  from  the  red  nucleus,  the  rubro-spinal  tract,  crosses  to 
the  opposite  side  (Fig.  59). 

At  the  level  of  the  inferior  colliculus  (Fig.  60  )  is  the  decussa- 
tion of  the  brachium  conjunctivum  (decussatio  brachii  conjunc- 
tivi) .     It  crosses  with  its  mate  to  reach  the  opposite  red  nucleus. 

At  the  level  of  the  isthmus  is  located  the  vestibular  com- 
missure composed  of  fibers  which  connect  the  vestibular  nuclei 
of  the  auditory  nerve.  Intermingled  with  the  above  bundles  of 
crossing  fibers  there  are  many  other  fibers  of  the  formatio 
reticularis. 

Tracts  of  Fibers  in  the  Tegmentum  (Figs.  58,  63  and  64). — 
In  the  reticulum  of  the  tegmentum  there  are  many  bundles 
of  longitudinal  fibers,  viz.,  the  medial  longitudinal,  tecto-spinal 
(anterior  and  lateral),  gustatory,  rubro-spinal,  thalamo- 
spinal,  thalamo-olivary,  spino-thalamic,  spino-tectal,  fillet, 
branchium  conjunctivum,  and  mesencephalic  root  of  the  trigem- 
inal nerve. 

The  medial  (or  posterior)  longitudinal  bundle  {fasciculus 
longitudinalis  medialis,  Fig.   58)  is  a  compact  strand  of  fibers 


MEDIAL   LONGITUDINAL  BUNDLE 


153 


running  along  the  median  raphe  just  ventral  to  the  central  gray 
substance.  In  Weigert-Pal  sections  it  shows  clearly  as  a  broad 
dark  triangle  1-2  mm.  thick  next  the  raphe.  The  tract  will 
be  found  in  the  same  relative  position  in  the  pons  and  medulla 
oblongata.  In  addition  to  several  very  small  strands  of  fibers 
which  will  be  explained  later,  the  medial  longitudinal  bundle  is 
functionally  composed  of  two  tracts:  (i)  An  afferent  bundle; 
and  (2)  an  efferent  bundle. 

I.  The   afferent  part   of   the   medial   longitudinal   bundle   is 


Fig.  58. — Transverse  section  through  the  corpora  mammillaria  and  the 
superior  colliculi  of  the  corpora  quadrigemina.  Natural  color,  not  stained. 
(Original.) 

a.  Lateral  geniculate  body.  b.  Thalamus,  c.  Medial  geniculate  body.  d.  Brachium 
superius.  e.  Pineal  body.  f.  Stratum  griseum  centrale.  g.  Superior  colliculus  of  corpora 
quad.  h.  Formatio  reticularis,  i.  Substantia  nigra,  j.  Basis  pedunculi.  k.  Medial  and 
lateral  nuclei  of  corpus  mammillare.  1.  Ventral  tegmental  decussation  (Foreli).  m.  Dorsal 
tegmental  decussation  (Meynerti).  n.  Medial  longitudinal  bundle,  o.  Optic  tract,  p. 
Red  nucleus,     q.   Medial  fillet. 

composed  of  T-b:ranched  fibers  derived  from  the  gray  matter 
of  the  spinal  cord  and  from  the  terminal  nuclei  of  sensory 
cerebral  nerves,  especially  from  the  vestibular  nuclei  of  both 
sides.  It  is  the  continuation  of  the  long  ascending  fibers  of 
the  anterior  fasciculus  propius.  Possibly  a  small  portion  of 
the  tract  runs  through  the  posterior  commissure  to  the  thalamus 
and  is  common  sensory  in  function;  but  the  major  part  of  it 
decussates  in  several  successive  strands  which  end  in  the 
opposite  motor  nuclei  of  the  cerebral  nerves.  The  function  of 
this  latter  part  is  reflex  and  coordinating. 


154  THE   CEREBRUM 

2.  The  descending  part  of  the  medial  longitudinal  bundle  is 
composed  chiefly  of  uncrossed  axones  from  the  large  cell-bodies 
in  the  nucleus  tegmenti  profundus  of  the  reticular  formation. 
This  is  the  anterior  reticulospinal  fasciculus.  Beginning  at  the 
nucleus  tegmenti  profundus,  which  is  the  nucleus  lateralis 
superior  of  the  reticular  formation,  it  receives  fibers  from  each 
reticular  nucleus  down  to  the  nucleus  lateralis  inferior  of  the 
medulla.  It  receives  the  largest  accession  of  fibers  in  the  pons, 
where  the  nucleus  lateralis  medius  and  the  three  nuclei  centrales 
are  located.  On  this  account  James  S.  Collier  suggests  that  it 
be  called  the  medial  ponto-spinal  tract.  It  has  been  traced 
through  the  anterior  fasciculus  proprius  to  the  lower  part  of  the 
spinal  cord.  Its  size  is  gradually  reduced  by  the  ending  of  a 
few  fibers  in  the  gray  substance  corresponding  to  each  segment 
of  the  cord.     It  is  associative  in  function. 

Muskens  and  others  describe  a  second  descending  strand  in 
the  medial  longitudinal  bundle.  Muskens  calls  it  the  commis- 
suro-medullary  fasciculus.  It  rises  from  two  nuclei:  the  nucleus 
of  the  posterior  commissure  (nucleus  of  Darkschewitsch)  and 
the  nucleus  of  the  medial  longitudinal  bundle.  The  nucleus 
of  the  posterior  commissure  is  in  the  prolongation  of  central  gray 
substance,  ventral  and  frontal  to  the  posterior  commissure;  the 
nucleus  of  the  medial  longitudinal  bundle  lies  still  farther  for- 
ward in  the  lateral  wall  of  the  third  ventricle,  just  caudal  to  the 
plane  of  the  mammillary  bodies.  The  fibers  rising  in  these 
nuclei  are  small  and  descend,  with  few  exceptions,  no  farther 
than  the  abducent  nucleus;  a  very  few  have  been  found  in  the 
cervical  cord. 

The  medial  longitudinal  bundle  is  an  association  tract  of  great 
importance  in  all  vertebrates,  especially  connecting  the  ves- 
tibular nuclei  with  the  nuclei  controlling  ocular  movements.  It 
contains  fibers  from  Deiter's  and  Bechterew's  nuclei  on  the  same 
side  and  from  the  chief  nucleus  of  Schwalbe  on  the  opposite  side. 
The  fibers  divide  T-like  and  the  branches  ascend  and  descend 
to  reach  the  motor  nuclei  of  the  brain-stem.  These  fibers  are 
medullated  in  the  fourth  and  fifth  months  with  the  fasciculus 
proprius  of  the  cord. 


ANTERIOR   TECTO-SPINAL   TRACT  155 

The  lateral  reticulospinal  fasciculus  begins  to  form  in  the 
lower  part  of  the  tegmentum.  It  is  composed  of  crossed  fibers 
from  the  nucleus  tegmenti  profundus  in  the  mid-brain.  Aug- 
mented by  axones  from  the  other  reticular  nuclei  in  the  pons  and 
medulla,  it  continues  downward  through  the  lateral  column  of 
the  spinal  cord.  Many  axones  of  the  reticular  nuclei  divide 
into  an  ascending  and  a  descending  ramus;  there  are  also 
ascending  fibers  in  the  tract  whose  origin  is  in  the  cord.  The 
latter  form  a  spino-reticular  fasciculus. 

In  the  mid-brain  the  medial  longitudinal  bundle  also  contains 
fibers  derived — (i)  from  the  oculomotor  nucleus,  which  descend 
to  the  pons,  and  enter  into  facial  nerve  through  which  they 
supply  the  muscles  of  expression  above  the  eye;  and  (2)  from 
the  nucleus  of  the  abducent  nerve.  Running  upward  and 
decussating,  the  latter  strand  of  fibers  terminates  in  the  opposite 
nucleus  of  the  oculomotor  nerve,  and  thus  innervates  the  medial 
rectus  of  that  eye.  This  strand  accounts  for  the  conjugate 
action  of  the  two  eyes  in  both  health  and  disease. 

Anterior  Tecto-spinal  Fasciculus  (anterior  or  ventral  longi- 
tudinal bundle  of  Heald). — The  anterior  tecto-spinal  bundle 
runs  ventro-lateral  to  the  medial  longitudinal  bundle  and  so 
close  to  it  as  to  be  considered  a  part  of  that  bundle  by  many 
anatomists.  It  is  not  a  separate  and  discrete  bundle  visible  in 
the  normal  adult  brain;  it  has  been  located  by  a  study  of  mye- 
linization  and  of  degeneration  following  lesions  of  the  tectiun 
(quadrigeminal  lamina)  (see  Figs.  60  and  64).  A  few  of  its 
fibers  rise  in  the  inferior  colliculus  but  its  chief  origin  is  in  the 
superior  colliculus  of  the  corpora  quadrigemina,  whence  it 
decussates  at  once  through  the  dorsal  tegmental  decussation 
(Meynerti)  and  descends  through  the  reticular  formation  of  the 
pons  and  medulla;  and  then  through  the  fissural  side  of  the 
anterior  column  of  the  spinal  cord  until  it  fades  away  in  the 
lumbar  region.  Its  fibers  end  in  the  gray  matter  of  the  cord 
on  both  sides  and  in  the  genetic  nuclei  of  cerebral  nerves;  but 
chiefly  in  the  nuclei  of  the  oculomotor,  trochlear  and  abducent 
nerves  and  in  the  cilio-spinal  center  of  the  spinal  cord.  In 
function  the  anterior  tecto-spinal  bundle  is  reflex;  it  is  connected 


iS6 


THE    CEREBRUM 


with  all  ocular  reflexes  which  are  excited  by  impulses  from  the 
retinae,  such  as  accommodation  for  distance,  pupillary  contrac- 
tion and  dilatation. 

The  lateral  tecto-spinal  fasciculus  rises  in  both  quadrigeminal 
coUicuH  on  the  same  side.  It  descends  without  crossing  through 
the  ventro-lateral  part  of  the  tegmentum,  just  dorsal  to  the 
medial  fillet  which  is  about  to  be  described.     In  its  course 


Fig.  59. — Section  of  the  mid-brain  through  superior  colliculi  and  the  apparent 
origin  of  the  oculomotor  nerve.  Natural  color.  {Original.) 
a.  Sulcus  lateralis  of  mid-brain,  b.  Red  nucleus,  c.  Medial  longitudinal  bundle,  d. 
Oculomotor  nucleus,  e.  Stratum  griseum  centrale.  f.  CoUiculus  superior  of  corpora 
quadrigemina.  g.  Formatio  reticularis,  h.  Medial  fillet,  i.  Medial  geniculate  body.  j. 
Optic  tract,  k.  Basis  pedunculi.  1.  Dorsal  tegmental  decussation  (Meynerti).  m. 
Ventral  tegmental  decussation  (Foreli).  n.  Fossa  interpeduncularis.  o.  Substantia 
nigra,  p.  Fronto-pontal  tract,  q.  3d.  N.  r.  Pyramidal  tract,  s.  Intermediate  tract. 
t.   Temporo-pontal  tract. 

through  the  pons,  medulla  and  cord  it  is  associated  with  the 
rubro-spinal  and  thalamo-spinal  tracts;  like  them  it  establishes 
connections  with  motor  nuclei. 

The  Fillet  or  Lemniscus  (Figs.  59,  63  and  64). — Near  the 
upper  end  of  the  pons,  in  the  ventral  part  of  the  formatio  reticu- 
laris, the  fillet,  or  lemniscus,  forms  a  very  broad  band  of  fibers 
on  either  side  of  the  median  raphe.  The  fillet  is  equal  in  width 
to  half  the  transverse  diameter  of  the  mid-brain.     It  continues 


FILLETS  157 

into  the  ventral  and  lateral  portions  of  the  tegmentum  in  the 
form  of  a  broad  crescentic  bundle  made  up  of  two  fasciculi, 
viz.,  the  medial  fillet,  and  the  lateral  fillet.  Farther  forward  a 
small  bundle  leaves  the  lateral  part  of  the  medial  fillet  and  runs 
up  to  the  superior  quadrigeminal  colliculus.  That  bundle  is 
called  the  superior  fillet. 

Function. — The  fillet  forms  a  segment  in  the  direct  sensory- 
tract.  It  carries  spinal  and  cerebral  impulses  of  the  tactile  and 
muscular  senses  to  the  corpora  quadrigemina  and  thalamus, 
and  auditory  impulses  to  the  inferior  quadrigeminal  colliculus. 


[i. 


T         .  ,  .>.  Medialis  {  L.  Superior. 

Lemniscus  \  ^     ^  ,. 

Lateralis 


Medial  Fillet  {Lemniscus  medialis,  Figs.  62  and  64). — The 
fibers  composing  the  medial  fillet  rise  chiefly  in  the  nucleus 
funiculi  gracilis  and  nucleus  funiculi  cuneati  of  the  opposite  side 
of  the  medulla  oblongata.  They  cross  over  in  the  fillet  decussa- 
tion of  the  medulla;  and,  excepting  a  small  bundle,  terminate 
in  the  lateral  nucleus  of  the  thalamus.  Fibers  are  added  from 
the  terminal  nuclei  of  sensory  cerebral  nerves  which  cross  the 
median  plane  and  enter  the  opposite  fillet.  Thus  connected 
with  all  common  sensory  nerves,  and  with  the  vestibular  nerve, 
it  enters  the  mid-brain  and  divides  into  two  parts.  A  small 
bundle  of  fibers  separating  from  the  lateral  part  and  running 
to  the  superior  quadrigeminal  colHculus,  forms  the  superior 
fillet.  It  associates  ocular  movements  with  sensations  from 
cerebral  and  spinal  nerves.  The  medial  fillet  continues  to  the 
lateral  nucleus  of  the  thalamus,  bearing  impressions  of  the  tac- 
tile and  the  muscular  sense.  From  the  thalamus  the  impulses 
are  carried  by  the  cortical  fillet  to  the  somaesthetic  area  of  the 
cortex. 

The  lateral  fillet  {lemniscus  lateralis)  forms  an  oblique  ridge 
on  the  lateral  border  of  the  tegmentum  (Fig.  41).  It  trends 
upward  and  inward  over  the  brachium  conjunctivum  to  the 
inferior  quadrigeminal  collicuH  where  some  of  its  fibers  termi- 
nate. A  few  fibers  continue  to  the  superior  colliculus.  Its 
function  is  auditory  conduction.     It  rises  chiefly  from  the  ventral 


iS8 


THE    CEREBRUM 


and  lateral  parts  of  the  cochlear  nucleus  (principally  the  oppo- 
site one)  and  ends  in  the  medial  geniculate  body,  the  fibers  being 
continued  beyond  the  inferior  colliculus  through  the  inferior 
quadrigeminal  brachium.  The  greater  number  of  its  fibers 
cross  through  the  trapezoid  body  and  medullary  stride,  some  are 
uncrossed  up  to  the  inferior  quadrigeminal  colliculus;  but  the 
acustic  path  is  entirely  crossed  above  that  level  (Ferrier  and 
Turner).     It  undergoes  partial  relay  in  the  nucleus  of  the  supe- 


d        e  f 


J  k 

Fig.  6o. — Section  of  the  mid-brain  cutting  the  inferior  coUiculi  of  the  corpora 
quadrigemina.  Unstained.  (Original.) 
a.  Sulcus  lateralis,  b.  Formatio  reticularis,  c.  Medial  longitudinal  bundle,  d. 
Nucleus  of  colliculus  inferior,  e.  Aqueductus  cerebri,  f.  Rubro-spinal  tract,  g.  Lateral 
fillet,  h.  Medial  fillet,  i.  Basis  pedunculi.  j.  Location  of  anterior  longitudinal  bundle. 
k.  Interpeduncular  fossa.     1.  Substantia  nigra,     m.  Decussation  of  brachia  conjunctiva. 


rior  olive  and  nucleus  of  the  trapezoid  body  on  both  sides  and 
the  nucleus  of  the  lateral  fillet  on  the  same  side. 

The  acustic  path  is  only  partially  relayed  in  the  inferior  col- 
liculus of  the  corpora  quadrigemina,  being  continued  directly 
into  the  brachium  inferius.  Auditory  conduction  therefore 
proceeds  from  the  inferior  colliculus  through  the  brachium  in- 
ferius to  the  medial  geniculate  body  and  then  through  the  acus- 
tic radiation  to  the  temporal  cortex.  Thus  the  lateral  fillet 
forms  the  second  stage  in  the  auditory  conduction  path.  The 
acustic  nerve  constitutes  the  first  stage,  the  fibers  of  the  lateral 


SPINO-THALAMIC   TRACT 


159 


fillet  the  second  stage,  the  brachium  inferius  the  third,  and  the 
acustic  radiation  the  fourth  stage.  The  last  stage  ends  in  the 
cortex  of  the  superior  and  the  transverse  temporal  gyri. 

The  spino-thalamic  fasciculus  (Figs.  63  and  64)  is  located  in 
the  region  of  the  nucleus  lateralis  superior.  It  is  a  loose  strand 
of  fibers  not  isolated  from  surrounding  structures.     The  spino- 


FiG.  61. — Section  of   mid-brain    through    superior  colliculi  of    quadrigeminal 

body.    Weigert-Pal  stain:  medullated  fibers  are  colored  black,  gray   substance 

remains  light. 

a.  Nucleus  of  oculomotor  nerve,  b.  Medial  longitudinal  bundle  and  anterior  tecto- 
spinal tract,  c.  Mesencephalic  root  of  the  trigeminal  nerve,  d.  Spino-thalamic  tract. 
e.  Medial  fillet,  f.  Red  nucleus,  g.  Base  of  the  cerebral  peduncle.  3.  Oculomotornerve. 
h.  Ventral  tegmental  decussation  formed  by  rubro-spinal  tracts,  i.  Central  gray  matter 
of  mid-brain,  j.  Superior  colliculus  of  quadrigeminal  body.  k.  Thalamo-olivary  tract. 
1.  Field  occupied  by  lateral  tecto-spinal,  lat.  reticulo-spinal,  rubro-spinal  and  thalamo- 
spinal  tracts,    m.  Substantia  nigra,     n.  Optic  tract. 

thalamic  tract  rises  in  the  gray  substance  of  the  spinal  cord  and 
in  the  terminal  nuclei  of  the  common  sensory  cerebral  nerves. 
Though  it  sends  some  fibers  to  the  quadrigeminal  bodies, 
spino-tectal  fasciculus,  and  to  the  substantia  nigra  and  the 
lentiform  nucleus,  its  chief  termination  is  in  the  lateral  nucleus 
of  the  thalamus.  It  is  sensory.  It  conducts  tactile,  pain  and 
temperature  impressions. 


i6o 


THE    CEREBRUM 


Brachium  Conjunctivum  {Superior  cerebellar  peduncle). — 
The  brachium  conjunctivum  forms  a  ridge  on  the  surface  near 
the  median  line  of  the  isthmus,  which  ends  above  at  the  inferior 
quadrigeminal  colli  cuius  (Fig.  41).  The  lateral  fillet  winds 
inward  over  its  upper  extremity.  It  is  joined  to  its  fellow  by  a 
sheet  of  white  matter,  the  superior  medullary  velum.     The  fibers 


Fig.  62. — Section  of  mid-brain  through  inferior  colliciUi  of  the  quadrigeminal 

body.     Weigert-Pa)  stain:  medullated  fibers  are  black,  gray  substance  is  light. 

a.  Decussating  fibers  of  lateral  fillet,  b.  Nucleus  of  trochlear  nerve,  c.  Inferior  coUi- 
culus  of  quadrigeminal  body.  d.  Region  of  lateral  tecto-spinal,  thalamo-spinal,  rubro- 
spinal and  lateral  reticulo-spinal  tracts,  e.  Decussation  of  brachia  conjunctiva,  f.  Medial 
fillet,  g.  Base  of  cerebral  peduncle,  h.  Interpeduncular  fossa,  i.  Medial  longitudinal 
bundle,  j.  Mesencephalic  root  of  trigeminal  nerve,  k.  Thalame  olivary  tract.  1.  Lateral 
fillet,     m.  Substantia  nigra. 


of  the  brachia  conjunctiva  bend  ventrally  beneath  the  inferior 
colliculus  of  the  corpora  quadrigemina  and,  for  the  most  part, 
decussate  anterior  to  the  cerebral  aqueduct,  through  the  median 
raphe  (Fig.  62).  These  crossed  fibers  with  the  few  uncrossed 
run  forward  toward  the  inferior  surface  of  the  thalamus,  where 
they  inclose  the  red  nucleus,  and  help  to  form  the  stratum 


♦  TEGMENTAL   TRACTS  l6l 

dorsale  of  the  hypothalamic  region  (Forel).  Many  of  the 
fibers  terminate  in  the  red  nucleus  and  from  it  others  rise  and 
proceed  forward  to  the  thalamus,  the  rubro-thalamic fasciculus. 
Though  most  of  the  brachium  conjunctivum  rises  in  the  cere- 
bellum and  forms  a  segment  of  an  indirect  sensory  tract,  it  also 
contains  a  few  visual  fibers,  probably  from  terminal  nuclei  of 
the  optic  nerve,  which  run  through  it  to  the  cerebellum.  This  is 
the  optic  nucleo-cerebellar  fasciculus. 

Rubro-spinal  fasciculus  (crossed  descending  tract  of  the 
red  nucleus). — Formed  by  axones  of  the  red  nucleus,  it  im- 
mediately crosses  through  the  ventral  tegmental  decussation 
(foreli)  and  proceeds  lateralward  to  the  angle  between  the 
medial  and  the  lateral  fillet  (Fig.  59).  In  the  lower  part  of 
the  mid-brain  it  is  imbedded  in  the  medial  part  of  the  lateral 
fillet.  The  rubro-spinal  tract  runs  through  the  medulla  and 
descends  in  the  spinal  cord  to  the  lumbar  region;  it  ends  in  the 
gray  crescent  and  in  motor  nuclei  of  the  brain-stem. 

Thalamo-spinal  Fasciculus. — The  rubro-spinal  tract,  from 
the  lowet  end  of  the  mid-brain  downward,  is  associated  with  a 
larger  bundle  originating  in  the  thalamus,  called  the  thalamo- 
spinal  fasciculus,  and  with  a  smaller  tract  from  the  quadri- 
geminal  colliculi  already  described  as  the  lateral  tecto-spinal 
fasciculus;  also  with  the  lateral  reticulo-spinal  fasciculus.  All 
these  fasciculi  terminate  in  relation  with  motor  nuclei,  cranial 
and  spinal  (Figs.  61  and  6t,). 

Thalamo-olivary  Fasciculus. — The  thalamo-olivary  bundle  is 
a  loose  strand  of  fibers  traversing  the  reticular  formation  lateral 
to  the  medial  longitudinal  bundle,  iji  the  upper  part  of  the  mid- 
brain ;  in  the  lower  region  of  the  mid-brain  it  runs  closer  to  the 
median  line  and  is  dorsal  to  the  fibers  of  the  brachium  conjuncti- 
vum as  they  are  about  to  enter  the  decussation.  The  thalamo- 
olivary  bundle  probably  rises  in  the  thalamus  and  ends  in  the 
olivary  nucleus  of  the  medulla.  It  becomes  a  distinct  visible 
tract  at  the  upper  end  of  the  pons  (Figs.  61  and  63). 

The  gustatory  fasciculus  has  been  traced  by  Otto  May  and 
Sir  Victor  Horsley  (Brain,  19 10).  The  taste  tract  runs  up 
through  the  mid-brain  dorso-lateral  to  the  medial  longitudinal 


l62 


THE   CEREBRUM 


bundle  and  chiefly  dorsal  to,  but  partly  intermingled  with,  the 
thalamo-olivary  fasciculus.  It  rises  in  the  nucleus  of  the  soli- 
tary tract  (nucleus  of  Nageotte)  near  the  junction  of  the  pons 
and  medulla;  its  termination  is  said  to  be  in  ''the  inner  part  of 
the  dorsal  third  of  the  nucleus  lateralis"  of  the  thalamus.  It 
was  first  observed  by  Probst  (1899)  and  Lewandowsky  (1904). 


b        a    3      k 


1  3  3 

Fig.  63. — Diagramatic  section  of  the  mid-brain  through  superior  colliculi  of 
the  quadrigeminal  body.  Motor  fibers  and  descending  tracts  are  red,  sensory- 
fibers  and  ascending  tracts  are  blue;  the  gray  matter  is  light. 

'a.  Cerebral  aqueduct,  b.  Nucleus  of  oculomotor  nerve,  c.  Gustatory  tract,  d. 
Spino-thalamic  tract,  e.  Inferior  quadrigeminal  brachium.  f.  Medial  fillet,  g.  Temporo- 
pontal  tract,  h.  Intermediate  tract,  i.  Fronto-pontal  tract,  j.  Medial  longitudinal 
bundle,  k.  Superior  coUiculus  giving  origin  to  the  anterior  tecto-spinal  tract  which  crosses 
in  the  dorsal  tegmental  decussation.  1.  Thalamo-olivary  tract,  m.  Field  occupied  by 
the  lateral  tecto-spinal,  the  lateral  reticulo-spinal,  and  the  thalamo-spinal  tracts,  n.  Red 
nucleus,  o.  Substantia  nigra,  p.  Optic  tract,  q.  Pyramidal  tract,  r.  Ventral  tegmental 
decussation  formed  by  rubro-spinal  tracts. 


The  mesencephalic  root  of  the  trigeminal  nerve  (Fig.  60) 
rises  in  the  lateral  part  of  the  central  gray  matter  in  the  mid- 
brain. It  is  a  motor  root.  It  occupies  a  thin  crescentic  area 
just  at  the  lateral  border  of  the  stratum  griseum  centrale  which 
thickens  as  it  proceeds  downward  toward  the  pons.  This  root 
extends  the  entire  length  of  the  mid-brain;  but  it  is  made  up  of 
very  few  fibers  in  the  upper  part  and  only  assumes  a  distinct 


MESENCEPHALIC  ROOT 


163 


shape  and  outline  when  the  level  of  the  inferior  quadrigeminal 
colliculus  is  reached.  It  is  continued  to  the  middle  of  the  pons 
in  the  same  lateral  relation  to  the  gray  substance;  and  medial 
to  the  brachium  conjunctivum  cerebelli  it  joins  the  main  part 
of  the  motor  root  and  bends  forward  toward  the  anterior  sur- 


FiG.  64. — Diagramatic  section  of  the  mid-brain  through  inferior  colliculi  of 
quadrigeminal  body.  Descending  tracts  are  red,  ascending  tracts  are  blue, 
gray  substance  is  light. 

a.  Decussating  fibers  of  lateral  fillet,  b.  Dorsal  longitudinal  bundle  of  Schutz.  c. 
Medial  longitudinal  bundle,  d.  Anterior  tecto-spinal  tract,  e.  Gustatory  tract.  £. 
Spino-thalamic  tract,  g.  Lateral  fillet,  h.  Medial  fillet,  i.  Intermediate  tract,  j. 
Base  of  cerebral  peduncle,  k.  Interpeduncular  fossa.  1.  Nucleus  of  trochlear  nerve. 
m.  Mesencephalic  root  of  the  trigeminal  nerve,  n.  Inferior  colliculus  of  quadrigeminal 
body.  o.  Thalamo-olivary  tract,  p.  Field  of  lateral  tecto-spinal,  thalamo-spinal,  rubro- 
spinal and  lateral  reticulo-spinal  tracts,  q.  Decussation  of  brachia  conjunctiva,  r. 
Substantia  nigra,     s.  Temporo-pontal  tract,     t.  Pronto-pontal  tract. 


face.  According  to  Otto  May  and  Horsley  the  mesencephalic 
root  extends  only  to  the  semilunar  ganglion.  It  is  intermingled 
in  the  mid-brain  with  ascending  fibers  of  the  sensory  root  of 
the  trigeminal  nerve;  these  fibers  terminate  about  the  cells  of 
the  mesencephalic  nucleus  and  are  probably  reflex  in  function. 
J.  B.  Johnston's  view  of  the  mesencephalic  nucleus  is  very 


164  THE    CEREBRUM 

different.  He  believes  it  represents  an  enveloped  ganglion  of 
pear-shaped  cells ;  that  its  fibers  correspond  to  the  peripheral 
processes  of  ganglion  cells  elsewhere;  and  that  they  are  afferent 
in  function  and  join  the  sensory  root  of  the  trigeminal  nerve. 

The  Quadrigeminal  Lamina  {Lamina  quadrigemina) . — The 
quadrigeminal  lamina  forms  the  fourth  great  division  of  the 
mid-brain.  It  rests  upon  the  dorsum  of  the  tegmenta,  entering 
into  a  large  part  of  the  posterior  surface,  of  the  mesencephalon. 
It  is  the  tectum.  A  crucial  groove  shapes  its  surface  into  four 
eminences,  called  colliculi  (colliculi  superiores  and  inferiores) 
(Fig.  56). 

The  colliculus  superior  of  either  side  is  larger  than  the  infe- 
rior colliculus  and  is  circular  in  outline.  It  has  resting  upon  its 
medial  half  the  pineal  body.  It  is  joined  to  the  lateral  genicu- 
late body  by  a  band  of  fibers  almost  entirely  concealed  by  the 
pulvinar  of  the  thalamus.  That  band  is  the  hrachium  superius. 
The  superior  colliculus  is  made  up  of  gray  substance  for  the 
most  part  (Figs.  58  and  61).  It  is  composed  of  a  superficial 
white  layer,  the  stratum  zonale,  and  a  thick  laminated  gray 
layer,  the  stratum  griseum.  Within  the  stratum  griseum  many 
fibers  end;  a  few  from  the  lateral  fillet,  spino-tectal  fasciculus, 
all  of  the  superior  fillet,  and  nearly  all  of  the  hrachium  superius. 
The  stratum  griseum  gives  origin  to  the  tecto-spinal  fasciculi 
and  probably  to  a  few  fibers  that  run  through  the  brachium 
superius  into  the  optic  nerve.  It  constitutes  an  optic-refiex 
center. 

The  colliculus  inferior  of  the  corpora  quadrigemina  is  elon- 
gated transversely  (Fig.  56).  It  is  joined  to  the  medial  genicu- 
late body  by  an  oblique  ridge,  called  the  hrachium  inferius  and 
it  forms  the  termination  of  two  ridges  that  approach  it  from 
below,  due  to  the  lateral  fillet,  and  the  brachium  conjunctivum 
of  the  cerebellum.  Its  surface  is  made  up  of  medullated  fibers 
continuous  with  the  lateral  fillet  and  brachium  inferius,  which 
forms  the  stratum  zonale;  gray  substance,  called  the  nucleus 
of  the  inferior  colliculus,  constitutes  its  deep  portion.  This 
nucleus  receives  a  part  of  the  lateral  fillet  and  brachium  inferius, 
and  gives  rise  to  a  portion  of  the  brachium  inferius  and  tecto- 


QUADRIGEMINAL  BRACHIA  iB^T      1 65 


spinal  fasciculi;  it  forms  a  partial  relay  in  the  acustic  path 
and  a  reflex  acustic  center. 

Brachium  Superius  (Figs.  55  and  56). — It  connects  the 
lateral  geniculate  body  with  the  superior  quadrigeminal 
colliculus;  but,  excepting  its  extreme  posterior  end,  it  is 
buried  in  the  substance  of  the  thalamus.  Its  course  is  anterior 
and  medial  to  the  medial  geniculate  body.  The  brachium 
superius  is  composed  chiefly  of  efferent  fibers  from  the  optic 
radiation,  a  tract  partially  relayed  in  the  lateral  geniculate 
body;  it  probably  contains  also  a  few  optic  fibers  from  the 
lateral  root  of  the  optic  tract  and  a  few  from  the  stratum 
griseum  of  the  superior  quadrigeminal  colliculus.  Optic 
reflex  impulses  are  conducted  by  the  brachium  superius. 

Brachium  Inferius  (Figs.  55  and  56). — The  inferior  arm, 
connecting  the  inferior  quadrigeminal  colliculus  and  the  medial 
geniculate  body,  is  visible  through  its  whole  length.  It  forms 
the  superior  boundary  of  the  triangle  of  the  lateral  fillet;  the 
lateral  fillet  and  the  sulcus  lateralis  of  the  mid-brain  form  the 
other  two  sides.  Two  strands  of  afferent  fibers  and  one  of 
efferent  fibers  make  up  the  brachium  inferius.  The  former  are 
the  lateral  fillet  (most  of  it)  and  the  axones  of  the  nucleus  col- 
liculi  inferioris;  these  terminate  in  the  medial  geniculate  body 
and  form  a  stage  of  the  acustic  path.  The  efferent  fibers  in 
the  brachium  inferius  are  axones  of  the  acustic  cortex  which 
descend  through  the  acustic  radiation  to  the  medial  geniculate 
body  and  continue  through  the  brachium  inferius  to  the  inferior 
colliculus. 

SECTION  III.  THE  STRUCTURE  OF  THE  CEREBRUM. 
ITS  GRAY  AND  WHITE  MATTER 

We  have  noticed  that  nerve  tissue  in  a  mass  is  made  up 
of  gray  and  white  substance.  The  gray  substance  contains 
the  bodies  of  the  nerve  cells  and  certain  nerve  processes,  which 
for  the  most  part  are  non-medullated;  the  white  substance  con- 
tains the  medulla  ted  nerve  processes  (axones  and  collaterals). 
The  body  and  all  the  processes  of  a  nerve  cell  constitute  a 
neurone.     These  neuronic  elements  are  supported  by  epiblastic 


i66 


THE   CEREBRUM 


Fig.  65. — Varieties  of  neurones  in  the  human  nervous  system. 
(After  Morris's  Anatomy.) 
A.  From  spinal  ganglion.  B.  From  ventral  horn  of  spinal  cord.  C.  Pyramidal  cell  from 
cerebral  cortex.  D.  Purkinje  cell  from  cerebellar  cortex.  E.  Golgi  cell  of  type  II  from 
spinal  ^  cord,  F.  Fusiform  cell  from  cerebral  cortex.  G.  Sympathetic,  a.  Axone.  d. 
Dendrites.  C.  Collateral  branches,  ad.  Apical  dendrites,  bd.  Basal  dendrites.  CC.  Central 
process,     p.  Peripheral  process,  the  dendrite. 


NEURONES  167 

and  mesoblastic  connective  tissues  and  nourished  by  a  very 
rich  blood  supply. 

Neurones. — The  one  essential  and  highly  specialized  ele- 
ment of  the  nervous  system  is  the  neurone,  which,  in  countless 
thousands,  makes  up  the  functionating  part  of  the  system. 
The  neurones  are  developed  from  the  columnar  cells  of  the 
neural  plate.  The  early  evolution  of  that  plate  into  neural 
tube  and  neural  crests  is  coincident  with  a  cleavage  in  the  life 
history  of  the  cells;  the  cells  of  the  neural  tube  develop  multi- 
polar neurones;  those  of  the  neural  crests  form  bipolar  neurones 
(see  note) . 

Note. — ^It  has  been  taught  hitherto  that  the  neural  crest  is  the  source  of 
multipolar  neurones  in  the  sympathetic  ganglia;  but  the  recent  investiga- 
tions of  A.  Kuntz  and  others  make  it  very  probable  that  all  the  sympathetic 
multipolars  are  carried  out  from  the  neural  tube  along  with  the  developing 
efferent  fibers  (see  Jour.  Comp.  Neurol.,  1914,  etc.). 

Thus  very  early  in  embryonic  life,  by  the  fifteenth  day,  the 
anlagen  of  the  two  great  classes  of  neurones  are  laid  down. 


Neurones 


I.  Multipolar 


\Se 


First  type 
Second  type 


T-T    T,.     ,  /  Fusiform 

II.  Bipolar  1  T.    T 

^  \  Pyriform 


As  soon  as  the  anlagen  are  laid  down  there  may  be  observed, 
near  the  lumen  of  the  neural  tube,  large  spherical  cells  with 
clear  cytoplasm  and  with  nuclei  possessing  mitotic  figures. 
These  spherical  cells  are  the  ^'germ  cells''  of  His.  By  their 
mitotic  division  the  germ  cells  produce  indifferent  daughter 
cells,  which  later  differentiate  into  spongioblasts  and  neuro- 
blasts. The  former  develop  the  ependyma  cells  and  these  in 
turn  the  neuroglia  cells.  The  neuroblasts  by  division  and 
differentiation  become  neurones.  From  the  deep  end  of  the 
neuroblast  (the  end  which  originally  was  next  the  mesoblast) 
a  pseudopod  is  thrown  out  which  develops  into  the  axone  of 
the  cell.  Later  in  the  life  of  the  cell  one  or  more  pseudopods 
are  projected  from  the  superficial  end  of  the  neuroblast;  they 
form  the  dendrites.  All  functionating  neurones  are  composed 
of  a  cell-body,  an  axone  and  one  or  more  dendrites.     The  bipolar 


i68 


THE   CEREBRUM 


^^ 


05 


Fig.  66. — Afferent  and  efferent  neurones — tigroid  bodies.     (Morris.) 


Fig.  67. — Pyramidal  and  ganglion  cells — neurofibrillae.     (Morris.) 


MULTIPOLAR  NEURONES  1 69 

neurones  have  but  one  dendrite;  the  multipolars  have  two  or 
more  dendrites. 

I.  Multipolar  Neurones. — Multipolar  neurones  are  found  in 
the  brain,  spinal  cord  and  sympathetic  ganglia.  They  are 
derived  from  the  neural  tube  (Figs.  65-68). 

The  cell-body  of  a  multipolar  neurone  may  be  pyramidal, 
fusiform,  stellate  or  pitcher-form  in  shape.  Its  size  varies 
from  2-135JU.  The  cell-body  is  made  up  of  a  mass  of  cytoplasm 
with  its  limiting  cell-wall  and  a  large  spherical  nucleus.  It  is 
contained  in  a  pericellular  lymph  space.  The  nucleus  is  central 
in  position  in  a  normal  neurone.  Its  most  visible  content  is  a 
nucleolus,  sometimes  more  than  one.  Among  several  other 
things,  it  contains  chromatin  imbedded  in  a  fluid  ground  sub- 
stance. The  cytoplasm  surrounds  the  nucleus  quite  uniformly, 
except  in  a  degenerated  neurone.  A  homogeneous  liquid  ground 
substance,  called  neuroplasm,  and  a  number  of  histologic  con- 
stituents make  up  the  cytoplasm  (E.  V.  Cowdry,  Amer.  Jour. 
Anat.,  Vols.  1 5  and  1 6) .  The  first  cytoplasmic  constituents  to  ap- 
pear are  small  granular  or  rod-hke  bodies  called  mitochondria. 
They  are  present  in  the  chick  within  the  first  24  hours  of  in- 
cubation, even  before  the  first  somite  is  developed.  The 
granules  measure  from  K-%  ix  and  the  rods  or  filaments 
2-4  /x  in  length.  The  mitochondria  are  universal  cell  constitu- 
ents in  the  tissues  of  all  vertebrates;  they  are  also  known  to  be 
present  in  several  invertebrates.  They  have  a  concentric  ar- 
rangement in  the  cytoplasm  and  a  parallel  arrangement  in  the 
medullated  fibers.  Meves'  iron  hematoxylin  stain,  or  CajaPs 
silver  nitrate,  or  the  Janus  green  intravitam  shows  them  satis- 
factorily. The  neurofibrillcB  (Fig.  67)  are  second  to  appear  in  the 
cytoplasm.  They  are  very  delicate  threads.  They  form  a 
reticulum  in  the  cell-body  and  continue  as  parallel  fibrils  in 
the  axone  and  dendrites.  They  are  coterminous  with  the 
neurone.  At  about  the  fortieth  hour  of  incubation  they  appear 
in  the  chick,  when  15  somites  are  present.  It  is  claimed  by 
some  authors  that  the  neurofibril! ae  are  the  conductive  elements 
in  the  neurone;  but  perhaps  the  neuroplasm  is  equally  impor- 
tant.   A  little  later  in  cell  life  (third  day  in  the  duck,  Marcora) 


lyo 


THE   CEREBRUM 


Fig.  68. — Motor  neurone.  (After  Barker.) 
a.h.  Axone-hillock  devoid  of  Nissl  bodies,  and  showing  fibrillation,  ax.  Axis  cylinder  or 
axone;  this  process  near  the  cell-body,  becomes  surrounded  by  myelin,  m.,  and  a  cellular 
sheath,  the  neurilemma,  the  latter  not  being  an  integral  part  of  the  neurone,  c.  Cytoplasm 
showing  Nissl  bodies  and  lighter  ground  substance,  d.  Protoplasmic  processes  (dendrites) 
containing  Nissl  bodies,  n.  Nucleus,  n'.  Nucleolus.  n.R.  Node  of^Ranvier.  s.f.  Side 
fibrils,  collaterals.  _  n.  of  n.  Nucleus  of  neurilemma  sheath,  tel.  Motor  end  plate  or  telo- 
dendrion.     m.  Striped  muscle  fiber.     s.L.  Segmentation  of  Lantermann. 


AXONES  171 

a  system  of  anastomosing  canals  can  be  detected  in  the  cyto- 
plasm. These  canals  of  Holmgren  open  into  the  pericellular 
lymph  space  which  surrounds  the  neurone.  They  probably 
convey  food  into  the  cell-body  and  waste  products  out  of  it. 
The  next  prominent  cytoplasmic  constituent  to  develop  is  the 
tigroid  or  Nissl  substance,  which  in  the  chick  is  found  in  the 
sixth  day  of  incubation  (Marcora).  It  stains  deeply  by  the 
Nissl  Method.  In  small  cells  (under  30  ju)  it  is  uniformly 
distributed,  but  is  aggregated  into  granules,  rod-like  and  cone- 
shape  masses  in  large  cell-bodies  (over  30  /x) ;  the  formation  of 
discrete  masses  appears  to  be  due  to  coagulation.  It  is  prob- 
ably a  food  substance  as  it  is  gradually  exhausted  by  continued 
stimulation  of  the  neurone.  More  or  less  pigment  is  frequently 
found  in  neurones,  especially  in  the  base  of  the  dendrites.  It 
is  said  to  be  more  abundant  in  the  aged  and  to  be  rarely  found 
in  the  young  cell,  except  in  a  few  special  situations.  Cowdry 
also  speaks  of  lipoid  globules  occurring  in  clumps  in  the  cell- 
body  and  along  its  processes.  They  have  a  reciprocal  relation 
to  the  mitochondria  and  may  be  derived  from  them.  He  does 
not  consider  them  an  evidence  of  degeneration.  The  last  cell 
content  to  be  mentioned  might  have  been  given  first,  viz.,  the 
organ  of  cell  division,  composed  of  the  archiplasm  sphere  and  its 
centrosome.  This  has  been  demonstrated  in  the  nerve  cells  of 
many  lower  animals  and  in  cells  of  the  cerebral  cortex,  spinal 
ganglia,  etc.,  in  man.  Fully  developed  nerve  cells  are  not  known 
to  undergo  division  and  this  organ  may  perform  some  other 
function  in  the  mature  neurone;  it  may  determine  the  discharge 
of  nerve  currents. 

The  axone,  neuraxone  or  axis-cylinder  of  a  multipolar 
neurone  is  the  first  process  to  develop;  it  attains  considerable 
length  before  there  is  any  evidence  of  dendrites.  It  grows  out 
of  what  was  primarily  the  deep  end  of  the  columnar  cell,  as 
its  function  in  the  simplest  forms  is  to  convey  to  muscles  or 
interior  organs  impulses  set  up  by  environmental  stimuli.  If 
the  axone  is  long,  the  neurone  is  of  the  first  type  (type  of  Deiters) ; 
if  the  axone  is  short  and  breaks  up  at  once  into  many  branches, 
it  constitutes  a  second  type  neurone  (type  of  Golgi).     The  axone 


172 


THE   CEREBRUM 


of  a  Type  II  neurone  branches  dichotomously  at  acute  angles 
near  the  cell-body,  arborizing  like  a  tree;  it  is  non-medullated; 
and  it  terminates  in  many  pointed  branches  in  contact  with 
other  neurones,  to  which  it  carries  its  impulses.  Some  of  the 
second  type  neurones  in  the  cerebral  cortex  have  a  brush-like 
axone  at  one  end  and  similar  dendrites  at  the  other;  those  are 
the  double-brush  cells  of  Cajal.  The  axone  of  a  Type  I  neurone 
is  relatively  long,  from  i-ioo  cm.     It  is  slender,  smooth  and 


Dendrites 


Nerve-cell 


-Neurilemma 


L,  Nerve-cell 


Dendrite 


Terminal 
branches 

A  B 

Fig.  69. — An  eflferent  neurone  and  an  afferent  neurone.     (After  Brubaker.) 

A.  Efiferent  neurone.     B.  Afferent  neurone. 


uniform  in  size;  it  is  fibrillar  in  character;  it  enters  into  a  fas- 
ciculus within  the  cerebrospinal  axis  and  into  a  nerve  outside 
the  axis;  it  gives  off  collaterals  at  right  angles  to  its  course, 
which  like  the  parent  axone  end  in  the  form  of  a  brush  or  tassel, 
called  end-brush  or  telodendrion;  the  end-brushes  form  contacts 
(synapses)  with  another  neurone,  a  muscle  cell  or  a  gland  cell, 
and  deliver  to  them  their  impulses.  The  telodendria  present 
various  modifications:  they  enter  into  motorial  end-plate  on 


MYELIN   SHEATHS 


173 


striated  voluntary  muscle;  they  form  ^'climbing  fibers"  which 
entwine  about  the  adjacent  neurone,  and  form  pericellular 
baskets  in  other  situations,  etc.  All  axones  are  cellifugal  in 
their  conduction  {cella — a  cell ;  and  fugere — to  flee  from) .  The 
axone  is  composed  chiefly  of  neurofibrillae  and  mitochondria 
imbedded  in  neuroplasm  and  surrounded  by  a  delicate  fibrous 
sheath,  the  axilemma.  Very  many  axones  become  meduUated 
in  the  cranio-spinal  system;  they  are  non-medullated  in  the 
S3rmpathetic  system.     The  myelin  sheath  begins   a   short  dis- 


FiG.  70. — MeduUated  and  non-medullated  nerve  fibers. 


tance  from  the  cell-body  and  terminates  proximal  to  the  telo- 
dendria.  It  is  a  solid,  continuous  sheath  inside  the  brain  and 
spinal  cord  and  in  the  optic  nerve  and  tracts.  The  meduUated 
nerves  which  possess  the  primitive  sheath  of  Schwann,  called  the 
neurolemma,  have  segmented  myelin  sheaths;  the  segments 
measure  from  0.08-1  mm.  in  length.  The  subdivisions  of 
these  segments  by  the  Schmidt-Lantermann  lines  or  cones  are 
probably  artefacts.  A  neurolemma  invests  the  axones  of  all 
peripheral  nerves  except  the  optic  and  olfactory;  the  former  is 
meduUated,  the  latter  is  not,  but  bundles  of  its  axones  are  sur- 


174 


THE   CEREBRUM 


rounded  by  a  sheath  like  a  neurolemma.  No  neurolemma  is 
found  within  the  brain  and  spinal  cord.  The  constrictions  of 
the  neurolemma  which  separate  the  segments  of  myelin  are  the 
nodes  of  Ranvier.  At  the  nodes  the  neurolemma  immediately 
invests  the  axilemma,  and  collaterals  are  given  off  at  these 
points. 

The  dendrites  of  a  multipolar  neurone  always  appear  later 
than  the  axone  of  the  same  cell.  The  pitcher-shaped  cells  of 
Purkinje  in  the  cerebellum  have  but  two  richly  branched 
dendrites;  other  multipolar  neurones  have   many   dendrites. 

B 


•Diagram  showing  development  of  neurones  in  the  spinal  cord. 
McMurrich  after  Schdfer. 

The  circles,  indifferent  cells;  circles  with  dots,  neuroglia  cells;  shaded  cells,  germinal  cells; 
circles  with  cross,  germinal  cells  in  mitosis;  black  cells,  nerve-cells. 


These  dendrites  taper  rapidly  and  branch  freely  at  acute  angles, 
like  a  tree,  hence  are  named  dendrites  (dendron — a  tree). 
They  are  partial  protrusions  of  cytoplasm,  which  arborize  close 
to  their  origin  and  possess  the  neurofibrillae  and  tigroid  substance 
of  the  cell-body.  In  contour  they  are  irregular,  being  gemu- 
lated  and  varicose.  They  terminate  in  fine  beaded  points  in 
contact  with  the  end  arborizations  of  other  neurones  from 
which  they  receive  impulses.  All  dendrites  conduct  impulses 
toward  the  cell-body,  all  possess  cellipetal  conduction  (cella — 
a   cell,    and   petere — to   seek).     The   dendrites   of   multipolar 


BIPOLAR   NEURONES  1 75 

neurones  are  destitute  of  both  the  neurolemma  and  the  medul- 
lary sheath. 

n.  Bipolar  neurones  (Figs.  65  and  69)  are  th^  peripheral 
neurones  of  the  sense  organs;  they  form  the  special  and  common 
sensory  nerves.  Bipolar  neurones  originate  in  the  neural  crest 
and  in  homologous  portions  of  epiblast  (see  note). 

Note. — The  dorso-lateral  plaques  (or  placodes)  of  epiblast  which  form 
the  vestibular  and  cochlear  ganglia  in  man  and  represent  the  anlagen  of  the 
nervus  lateralis  in  gill-breathing  animals:  the  epibranchial  plaques  that 
form  the  ganglia  of  the  nerves  of  taste  (the  glosso-palatine  or  intermediate 
and  the  glosso-pharyngeal) :  and  the  epiblastic  plaques  in  the  olfactory  pits 
which  constitute  the  ganglia  of  the  olfactory  nerves  are  all  derived  from 
out-lying  parts  of  the  neural  plate — parts  homologous  with  the  neural  crest. 
And  the  retina,  which  in  man  is  a  diverticulum  of  the  prosencephalon,  is 
derived  from  epiblast  corresponding  to  neural  crest;  this  part  of  the  neural 
crest  is  included  in  the  formation  of  the  cephalic  end  of  the  neural  tube 
because  of  its  great  size  in  man.  So  the  bipolar  neurones  of  the  olfactory, 
optic,  gustatory  and  acustic  nerves,  which  in  man  appear  not  to  originate 
in  the  neural  crest,  rise  from  parts  homologous  with  it. 

The  most  primitive  and  embryonic  hipolars  are  those  whose 
cell-bodies  form  the  acustic  and  olfactory  ganglia  and  the  in- 
ternal nuclear  layer  of  the  retina  (the  layer  of  bipolars).  They 
have  fusiform  or  spindle-shaped  cell-bodies.  The  specialized 
bipolar  neurones  have  pear-shaped  bodies  which  form  the  gan- 
glia of  the  common  sensory  and  taste  nerves.  The  bodies  of 
the  bipolars  have  the  same  cellular  constituents  as  the  multi- 
polar neurones;  and  the  life  histories  of  the  two  neurones  are 
identical  both  as  to  the  points  of  origin  of  the  axone  and  the 
dendrite  and  as  to  sequence  in  the  time  of  their  development. 
The  bodies  of  bipolar  neurones  are  inclosed  in  a  nucleated  cap- 
sule continuous  with  the  neurolemma  of  the  processes.  The 
neurolemma  invests  the  neurone  from  the  surface  of  the  cere- 
brospinal axis  to  the  vicinity  of  the  telodendria;  it  bounds  a 
perineural  lymph  space. 

The  fusiform  bipolar  neurones  are  prolonged  at  opposite 
poles  into  two  processes,  the  axone  and  dendrite.  The  axone 
grows  out  of  the  deep  end  of  the  neuroblast  into  the  brain. 
It  divides  into  T-branches  which  give  off  several  collaterals 


176  THE    CEREBRUM 

ending  in  telodendria;  the  telodendria  form  synapses  with  the 
neurones  of  a  terminal  nucleus,  to  which  the  impulses  travers- 
ing the  axone  are  delivered  (celHfuga]  conduction). 

In  the  olfactory  nerve  the  axones  are  very  slender  (0.5  fj,). 
They  are  varicose,  non-medullated  and  are  collected  into 
twenty  or  more  bundles  that  are  invested  by  a  nucleated  sheath 
like  a  neurolemma.'     They  end  in  the  olfactory  bulb. 

The  optic  nerve  morphologically  is  really  formed  by  the 
bipolars  of  the  retina,  whose  axones  are  very  short;  they  end 
in  contact  with  the  ganglionar  neurones,  whence  the  optic 
nerve,  as  it  is  ordinarily  described,  takes  its  origin.  The 
fibers  of  the  optic  nerve  and  tracts  correspond  to  a  brain  tract, 
so  they  have  no  neurolemma;  but  they  are  large  and  meduUated 
and  are  imbedded  in  neuroglia.  They  terminate  in  the  inter- 
brain  and  mid-brain. 

The  axones  of  the  cochlear  and  vestibular  nerves  which 
rise  in  the  spiral  and  vestibular  ganglia  are  medullated  fibers. 
They  carry  impulses  of  hearing  and  equilibrium  to  their  terminal 
nuclei  in  the  medulla  oblongata. 

The  dendrites  of  fusiform  bipolar  neurones  are  single  and 
cellipetal  in  conduction.  Those  from  the  olfactory  ganglion 
are  very  short  (0.02  mm.).  In  the  form  of  a  tuft  of  hairs,  they 
protrude  sHghtly  through  the  mucous  membrane  into  the  nasal 
fossa.  The  dendrites  of  the  retinal  bipolars  measure  from 
0.01-0.015  mm.  Branching  they  form  contacts  with  the  rods 
and  cones,  from  which  they  receive  the  visual  impulses.  The 
dendrites  of  the  spiral  and  vestibular  neurones  are  longer, 
measuring  a  few  millimeters  in  length.  They  are  in  part  medul- 
lated. They  extend  from  the  spiral  ganglion  to  the  hair  cells  of 
the  spiral  organ  of  Corti  and  from  the  vestibular  ganglion  to  the 
hair  cells  of  the  acustic  spots  and  ampullary  crests  within  the 
labyrinth.  From  the  hair  cells  they  receive  the  impulses  of 
hearing  and  equilibrium. 

Pyriform  or  Pear-shaped  Bipolar  Neurones. — The  pear- 
shaped  bipolars  are  the  neurones  of  the  common  sensory  and 
taste  nerves:  their  cell-bodies  form  the  ganglia  of  those  nerves; 
their  processes  constitute  the  fibers  of  them.     Formerly  these 


PEAR-SHAPED   NEURONES  1 77 

bipolars  were  called  unipolar  neurones  with  two  axones,  in 
accordance  with  their  mature  appearances;  but  their  embry- 
ology and  their  phylogeny  show  them  to  be  true  bipolars,  and 
the  evolution  of  the  peripheral  process  and  its  cellipetal  conduc- 
tion furnish  abundant  reason  for  calling  it  a  'dendrite"  rather 
than  an  *'axone  with  reversed  polarity  (Figs.  65A,  66  and  67)." 

The  cell-body  of  the  pear-shaped  bipolar  neurone  is  very 
large  (170  /i).  It  is  the  product  of  an  evolution  which  con- 
tinues after  the  simple  fusiform  stage  is  reached:  the  spindle- 
shape  is  the  permanent  form  in  the  cyclostome  and  amphyoxus 
(J.  B.  Johnston),  as  it  is  the  embryonic  form  in  man.  In  the 
bony  fishes  some  of  the  peripheral  sensory  neurones  become 
pear-shaped;  in  man  practically  all  take  this  form.  The  cell- 
body  becomes  almost  spherical  in  this  process;  the  two  processes 
shift  to  one  side  of  the  body;  and,  by  the  growth  of  the  axone 
and  dendrite,  the  body  is  pushed  in  the  direction  of  least  re- 
sistance, the  two  processes  are  approximated  and,  therefore, 
appear  connected  with  the  body  by  a  common  stem.  The 
common  stem  joins  the  cell-body  at  a  highly  developed  axone- 
hillock  and,  after  a  sinuous  course  of  i  or  2  mm.,  it  bifurcates 
into  its  two  original  parts,  axone  and  dendrite.  The  nuclear 
and  cytoplasmic  constituents  of  the  pear-shaped  bipolar  neu- 
rones are  identical  in  kind  with  those  in  multipolars. 

The  axones  of  pear-shaped  bipolar  neurones  form  the  roots 
of  the  common  sensory  and  taste  nerves.  They  extend  to  the 
surface  of  the  cerebrospinal  axis  covered  by  a  neurolemma  and  a 
segmented  myelin  sheath,  if  meduUated.  There  the  neuro- 
lemma ends,  but  the  fibers  enter  the  axis  with  solid  medullary 
sheaths.  Inside  the  axis  the  axones  divide  into  ascending  and 
descending  T-branches,  which  give  off  collaterals ;  after  a  course 
of  varying  length  the  myelin  sheath  is  lost,  the  telodendria  are 
formed  and  synapses  are  established  with  neurones  of  the  brain 
or  cord  to  which  the  afferent  impulses  are  delivered.  Cellifugal 
conduction  is  again  exemplified  in  the  axone. 

The  dendrite  of  a  pear-shaped  bipolar  neurone  is  very  long 
and  slender.  It  extends  from  the  common  stem  of  a  cell-body 
in  a  spinal  or  cranial  ganglion  out  to  some  part  of  the  periphery. 


178  THE   CEREBRUM 

It  is  an  afferent  or  sensory  fiber  in  some  cranial  or  spinal  nerve. 
In  every  microscopic  particular  it  is  like  the  axone  of  a  first  type 
multipolar  neurone  (q.v.).  Its  telodendria  are  free  among  the 
cells  of  the  various  tissues  or  they  are  encapsulated  by  special- 
ized end-organs,  viz.,  the  tactile,  bulbous  and  lamellous  cor- 
puscles, and  the  neuro-muscular  and  neuro-tendinous  spindles. 
The  endings  are  adapted  to  the  reception  of  external  and  in- 
ternal stimuli;  the  impulses  thus  excited  travel  up  the  dendrite 
to  the  cell-body  and  continue  through  the  axone  into  the 
cerebrospinal  axis.  Like  all  dendrites,  these  possess  cellipetal 
conduction. 

The  neurone  doctrine  maintains  that  every  neurone  is  de- 
rived from  an  epiblastic  cell;  that  nerve  fibers  are  outgrowths 
of  the  cell-body;  and  that  the  individual  neurones  in  all  higher 
animals  are  related  to  each  other  only  by  contact  (see  ^'Neu- 
rones and  the  Neurone  Concept" — Santee:  Illinois  Medical 
Journal,  June,  191 2). 

The  myelin  sheath  of  axones  and  dendrites,  which  is  devel- 
oped as  the  neurone  begins  to  functionate,  is  imbedded  in 
neuroglia  within  the  optic  and  acustic  nerves,  and  in  the  brain  and 
spinal  cord;  but,  elsewhere,  is  surrounded  by  the  neurolemma 
(Schwann)  and  the  fibrous  sheath  of  Henle.  The  fibers  of  the 
olfactory  nerve  and  most  sympathetic  fibers  are  not  medullated, 
but  the  latter  possess  the  fibrous  sheath.  Near  the  cell-body 
and  near  the  end-tuft  the  processes  are  naked,  having  neither 
the  fibrous  nor  the  medullary  sheath.  ''Myelin  is  a  mixture  of 
complex  fats  and  lipoid  substances,  some  of  which  are  combined 
with  sugar"  (F.  T.  Lewis).  It  is  an  emulsion  supported  by  a 
delicate  reticulum  of  neurokeratin.  In  preserved  specimens  it 
shrinks  greatly  and  fissures.  Ether  and  alcohol  dissolve  the 
fats  but  not  the  reticulum,  which  is  revealed  by  such  treatment. 
Osmic  acid  stains  myelin  very  black  (Figs.  68,  69  and  70). 

Types  of  Neurones. — i.  The  first  type  has  a  long  axone, 
which  preserves  its  identity,  though  it  may  givQ  off  many  col- 
laterals. Found  in  fasciculi  of  brain  and  spinal  cord  and  in 
nerves  (Deiters)  (Figs.  65  and  68). 

2.  The  second  type  has  a  short  axone,  breaking  at  once  into 


ORDERS  AND   FUNCTIONS   OF   NEURONES 


179 


branches  of  apparently  equal  importance,  the  dendraxone. 
Found  in  cerebrum  and  cerebellum  (Golgi). 

There  are  probably  no  neurones  that  have  more  than  one 
axone.  The  double-brush  cells  of  Cajal  are  really  second  type 
cells. 

Orders  of  Neurones.— i.  The  first  order  has  distal  process  in 
relation  with  the  periphery,  as  spinal-ganglion  and  anterior  col- 
umna  neurones,  and  conducts  from  the  periphery  or  to  it. 

2.  The  second  order  has  cell-body  or  distal  process  in  relation 


Fasciculus  cuneatus 


Cephalic  branch  of  spinal  ganglion  neurone 
Dorsal  (posterior)  root 


Fig.  72. — Illustrating  functions  of  neurones.     (Morris.) 

with  neurone  of  first  order.  It  conducts  to  a  neurone  of  the 
first  order  or  conducts  centrally  from  it.  In  like  manner  there 
are  neurones  of  the  third,  fourth,  fifth  order,  etc. 

Functions  of  Neurones. — i.  Afferent.  2.  Associative.  3. 
Efferent.  In  afferent  conduction  paths  the  dendritic  side  of 
each  neurone  is  directed  toward  the  periphery  to  receive  the  in- 
coming impulses :  the  axones  are  directed  toward  the  periphery 
in  efferent  paths  in  order  to  carry  the  impulses  directly  to 
striated  muscle,  or  to  a  ganglion,  through  which  it  reaches 


l8o  THE    CEREBEUM 

smooth  muscle  (also  heart  muscle)  and  gland  cells.  Two  such 
paths  may  be  connected  by  associative  neurones  and  a  reflex 
arc  established  (Fig.  72). 

Degeneration. — Augustus  V.  Waller  discovered  in  1850  that 
a  nerve  fiber,  severed  from  the  cell-body  out  of  which  it  grew, 
soon  undergoes  degeneration.  This  degeneration  of  Waller  is 
evident  in  about  48  hours  and  is  almost  complete  by  the  four- 
teenth day.  It  consists  of  a  disintegration  of  the  myelin  into 
droplets  and  globules  of  granular  lipoid  substances  which  stain 
very  deeply  with  Marchi's  fluid;  of  a  breaking  up  and  gradual 
disappearance  of  the  nerve  fiber;  and,  later,  of  an  absorption  of 
the  myehn  debris.  In  peripheral  nerves  having  a  neurolemma, 
there  is  also  a  proliferation  of  the  nuclei  of  the  neurolemma  and 
the  formation  of  a  "band  fiber,"  which  guides  the  "cone  of 
growth  "  in  regeneration.  That  part  of  the  fiber  connected  with 
the  cell-body,  the  central  stump,  does  not  suffer  this  Wallerian 
degeneration.  In  peripheral  nerves  the  central  stump  may 
very  soon  show  evidence  of  regeneration;  but  within  the  brain 
and  spinal  cord  regeneration  does  not  take  place  with  any  degree 
of  perfection  in  man.  On  the  contrary,  signs  of  degeneration 
slowly  appear  in  the  cell-body  after  10  days  and  grow  more 
evident  to  the  end  of  the  third  or  fourth  week.  This  degenera- 
tion consists  in  a  shifting  of  the  nucleus  to  an  eccentric  position 
and  a  breaking  up  and  disappearance  of  the  Nissl  substance,  a 
chroma tolysis.  It  is  called  Nissl  degeneration.  In  the  cerebro- 
spinal axis  this  Nissl  degeneration  is  usually  followed  by  grad- 
ual atrophy  of  the  whole  neurone  and,  after  many  months  or  a 
period  of  years,  by  entire  disappearance  of  it.  Nissl  degenera- 
tion, followed  by  gradual  atrophy  and  disappearance,  also 
occurs  when  neurones  are  deprived  of  their  function  by  any 
cause,  as  the  removal  of  a  limb  or  organ  or  the  destruction  of 
any  group  of  neurones  in  a  chain. 

Regeneration. — If  a  neurone  is  destroyed  in  man  it  is  not 
replaced  by  proliferation  of  other  neurones;  mature  neurones  do 
not  exhibit  mitotic  or  direct  division.  However,  complete 
regeneration  may  follow  the  cutting  of  peripheral  nerves. 
The  most  interesting  proof  of  this  is  furnished  by  the  experi- 


REGENERATION  OF  NEURONES 


l8l 


ment  of  Henry  Head,  in  which  the  superficial  radial  nerve  of  his 
left  arm  was  cut  at  the  elbow  and  the  recovery  carefully  observed 
through  567  days  (Head  and  Rivers:  Brain,  Vol.  31,  1908). 
The  regeneration  of  a  nerve  fiber  (axone  or  dendrite)  is  similar 


Fig.  73. — A  section  through  the  spinal  cord  of  a  human  fetus  23  cm.  in  length. 
Showing  the  central  canal  with  its  substantia  gelatinosa  centralis,  neuroglia 
cells  and  ependyma  cells.     (After  Lenhossek.    Gordinier's  Nervous  System.) 


to  its  original  development.  A  soft  "cone  of  growth"  forms 
on  the  distal  end  of  the  central  stump,  the  part  connected  with 
the  cell-body;  this  growing  cone  by  amoeboid  movement,  that 
is,  by  sending  out  and  withdrawing  one  psuedopod  after  an- 
other, gradually  insinuates  itself  between  the  cells  of  the  "band 


1 82  THE   CEREBRUM 

fiber"  until  it  reaches  every  point  touched  by  the  original  fiber. 
It  appears  to  be  directed  by  a  strong  neurotropic  force  residing 
chiefly  in  the  cells  of  the  ''band  fiber." 

Sustentacular  Tissue  (Fig.  73). — In  the  brain  and  spinal  cord 
and  in  the  optic  nerves  three  forms  of  sustentacular  tissue  are 
found  supporting  the  neurones,  viz. :  ependyma,  neuroglia  and 
ordinary  connective  tissue.  The  first  two  are  derived  from 
epiblast,  the  last  is  of  mesoblastic  origin. 

.  The  ependyma  cells  form  the  earliest  support  for  the  embryonic 
neurones  of  the  brain  and  cord;  in  the  adult  they  merely  line  the 
ventricles.  They  are  columnar  epithelial  cells  which  reach  from 
the  internal  to  the  external  limiting  membrane.  The  internal 
parts  of  these  cells  containing  the  nuclei  remain  fixed  for  a  time 
in  contact  with  the  internal  limiting  membrane;  the  external 
parts,  by  the  growth  of  the  neural  tube  in  thickness,  become 
drawn  out  into  tenuous  fibers  which  radiate  from  the  central 
canal  to  the  exterior  surface.  Thus  there  is  formed  a  radial 
^'sustentacular  apparatus"  with  a  "nuclear  zone"  next  the 
central  canal.  This  radial  framework  is  further  elaborated  by 
the  development  of  spines  and  varicosities  along  the  course  of 
the  tenuous  fibers  and  by  the  arborization  of  those  fibers  in 
their  peripheral  portions.  In  the  chick  at  the  fourth  day  of 
incubation,  there  is  no  other  sustentacular  tissue  in  the  neural 
tube  (Villiger).  Following  the  four-day  stage,  two  processes 
occur  simultaneously,  viz.,  migration  of  cell-bodies  from  the 
nuclear  zone  and  disappearance  of  the  radial  framework.  The 
cell-bodies  remaining  in  the  nuclear  zone  develop  cilia  and 
become  the  permanent  ependyma  cells  of  the  adult;  the  migrat- 
ing cells  form  the  neuroglia. 

The  neuroglia  cells,  as  just  stated,  arise  from  the  migrating 
ependyma  cells.  According  to  Villiger,  these  migrating  cells 
appear  in  the  chick  on  the  tenth  day  of  incubation.  They  lose 
their  connection  with  the  limiting  membranes,  to  a  large  extent; 
and,  branching,  become  typical  spider  cells  with  short,  stocky 
branches  or  long  filamentous  branches,  constituting  the  short- 
rayed  and  long-rayed  neuroglia  cells.  Those  maintaining  their 
connection  with  the  limiting  membranes  give  off  long,  parallel 


GROUPING   OF   NEURONES  1 83 

filamentous  branches,  which  at  the  surface  expand  and  fuse  with 
one  another.     The  latter  are  the  arborescent  neuroglia  cells. 

Connective-tissue  Network. — That  is  of  mesoblastic  origin  and 
is  formed  by  branching  processes  from  the  inner  surface  of  the 
pia  mater.  It  transmits  the  blood-vessels  into  the  nervous 
substance. 

The  neurones  constitute  53  per  cent,  of  the  brain  and  cord 
(cell-bodies,  6  per  cent.)  and  the  sustentacular  tissue  47  per  cent. 
(Donaldson). 

Grouping  of  Neurones. — The  bodies  of  neurones  are  massed 
in  certain  situations  forming  the  cortex  of  the  cerebrum  and 
cerebellum,  the  basal  complex  nuclei  (ganglia),  the  cranial  and 
spinal  nerve-nuclei,  and  the  sensory  and  sympathetic  ganglia. 

A  group  of  neurone-bodies  located  outside  the  cerebrospinal 
axis  is  called  a  ganglion;  it  is  called  a  nucleus  inside  the  axis. 
A  ganglion  is  sensory  if  bipolar  neurones  compose  it  and  its 
processes  form  a  sensory  nerve  or  the  sensory  part  of  a  mixed 
nerve;  such  a  ganglion  is  located  on  an  afferent  nerve.  If  a 
ganglion  is  made  up  chiefly  of  multiploar  neurones  whose  axones 
supply  involuntary  muscle  or  glands,  it  is  a  sympathetic  gang- 
lion (autonomic  ganglion).  According  to  Dogiel  sympathetic 
gangha  contain  some  afferent  neurones  and  Robert  B.  Bean  has 
demonstrated  afferent  and  efferent  neurones  in  the  geniculate, 
petrosal  and  jugular  ganglia,  so  there  is  a  third  class,  called  the 
mixed  ganglia.  The  sympathetic  and  mixed  ganglia  are  to  a 
large  extent  self -regulating  centers  (autonomic  centers). 

f  Sensory 
Ganglia  I  Sympathetic 
[  Mixed. 

A  group  of  neurone-bodies  within  the  brain  or  cord  consti- 
tutes a  nucleus.  Nuclei  may  be  very  large,  as  the  basal  com- 
plex nuclei  of  the  cerebrum,  the  cerebral  cortex,  etc.,  or  much 
smaller  as  is  illustrated  by  the  cranial  and  spinal  nerve-nuclei. 
The  nucleus  of  a  peripheral  nerve  connected  with  the  functions 
of  the  extremities  or  body  wall  is  a  somatic  nucleus  {soma-hody) ; 
a  nucleus  that  sends  impulses  to  smooth  muscle,  glands  or  the 


1 84  THE    CEREBRUM 

great  viscera,  or  receives  impulses  from  them  is  a  visceral  nucleus. 
If  the  axones  of  a  nucleus  form  an  efferent  nerve,  that  is  a 
nucleus  of  origin,  a  genetic  nucleus  {genesis-oxigm) ;  it  is  somatic 
if  it  supplies  striated  muscle  and  visceral  if,  through  a  sympa- 
thetic ganglion,  it  innervates  smooth  muscle,  heart  muscle  or  a 
gland.  Edward  F.  Malone  and  others  have  discovered  that  the 
cell -bodies  of  somatic  nuclei  of  origin  possess  a  much  larger 
mass  of  cytoplasm  than  the  visceral  genetic  nuclei  and  have 
more  definite  tigroid  aggregations;  also  that  the  cell-bodies  of 
the  "nucleus  cardiacus,"  which  innervate  striated  heart  muscle, 
are  intermediate  in  position  between  those  supplying  voluntary 
and  smooth  muscle  (Amer.  Jour.  Anat.,  Vol.  13,  1913). 
Other  nuclei  receive  the  axonic  end-brushes  of  sensory  nerves. 
These  are  terminal  nuclei.  They  from  only  synapses  with  the 
axones  of  afferent  nerves;  there  is  no  continuity  between  them. 
A  terminal  nucleus  is  somatic  or  visceral  according  to  the  per- 
ipheral relations  of  the  nerve  which  it  receives.  Furthermore,  a 
visceral  nucleus  of  termination  is  merely  a  part  of  a  reflex 
arc;  a  somatic  nucleus  of  termination  is  the  same  and  in  addition 
is  a  part  of  the  path  to  the  center  of  consciousness,  where  the 
impulses  become  sensations. 

(Somatic       \  Genetic  and  Terminal 
Visceral       {  Genetic  and  Terminal 

Neurone  Cycles. — A  strand  of  nerve  fibers,  medullated  or 
non-medullated,  constituting  a  distinct  and  separate  bundle  and 
located  outside  the  cerebrospinal  axis  is  a  nerve.  It  may  be 
afferent,  efferent  or  mixed  in  function.  A  spinal  nerve  is 
connected  with  the  central  axis  by  a  ventral  and  a  dorsal  root. 
The  ventral  root  rises  in  the  axis  and  is  efferent.  The  dorsal  root, 
rising  in  the  ganglion  located  on  the  root,  enters  the  cerebro- 
spinal axis  and  terminates  within  it;  the  dorsal  root  is  afferent. 
The  afferent  and  efferent  roots  are  joined  together  in  the  cord, 
either  directly  or  by  intercalated  second-type  neurones,  and  the 
simple  reflex  arc  or  neurone  cycle  is  the  result.  Within  the 
cerebrospinal  axis,  a  bundle  of  fibers  having  the  same  general 


NEURONE   CYCLES  1 85 

origin,  destination  and  function  is  called  a  fasciculus  or  tract; 
for  example,  the  pyramidal  tract  or  cerebrospinal  fasciculus, 
the  fasciculus  gracilis,  etc.  Two  or  more  fasciculi  massed  into  a 
complex  bundle  form  a  funiculus  or  column;  as  the  anterior, 
lateral  and  posterior  funiculi  or  columns  of  the  spinal  cord. 
Fasciculi  which  join  different  parts  or  levels  of  the  nervous 
system  on  the  same  side  of  the  median  plane  are  called  associa- 
tion fasciculi.  Those  are  commissural  bundles  which  extend 
transversely  through  the  median  plane  and  connect  opposite 
sides;  they  form  the  commissures.  When  a  pair  of  longitu- 
dinal bundles,  one  on  either  side,  cross  each  other  obliquely 
through  the  median  plane,  they  constitute  a  decussation. 

A  nerve  or  a  nerve  and  one  or  more  fasciculi  in  the  cerebro- 
spinal axis,  linked  together  end  to  end,  make  up  a  conduction 
path.  The  successive  orders  of  neurones  in  the  path  are  linked 
by  contact  (synapsis).  In  an  efferent  path  the  axones  of  one 
order  touch  the  dendrites  and  cell-bodies  of  the  next  order  below 
them;  e.g.,  the  fibers  of  the  pyramidal  tract  (third  order)  form 
contacts  with  the  intercalated  neurones  in  the  cord  (second 
order)  and  these  with  the  motor  nerve  neurones  (first  order). 
While  the  axones  touch  the  dendritic  side  of  the  neurones  next 
in  order  above  them  in  an  afferent  conduction  path,  in  the  fol- 
lowing order:  the  sensory  fibers  of  a  spinal  nerve  (as  a  sacral), 
the  dorsal  root  of  that  nerve  and  the  fasciculus  gracilis  (first 
order);  the  medial  fillet  neurones  (second  order),  and  the  thal- 
amo-cortical  neurones  (third  order).  Afferent  and  efferent 
conduction  paths  are  very  numerous.  To  be  fully  functional 
they  must  be  linked  together  into  cycles  or  arcs;  so  that,  for 
instance,  the  afferent  path  from  a  muscle,  and  the  joints  moved 
by  it,  is  connected  into  a  circuit  with  the  efferent  path  which 
bears  the  motor  impulses  to  that  muscle.  Such  linking  of  affer- 
ent and  efferent  paths  occurs  at  various  levels  in  the  nervous 
system.  In  the  spinal  cord  and  cranial  nerve  nuclei  the 
simplest  reflex  arcs  are  completed.  Longer  and  more  compli- 
cated arcs  are  formed  by  associations  in  the  medulla,  in  the 
basal  nuclei  of  the  cerebrum,  in  the  nuclei  and  cortex  of  the 
cerebellum  and  in  the  cerebral  cortex.     In  fact  the  nervous 


1 86  THE    CEREBRUM 

system  is  very  largely  made  up  of  reflex  arcs  and  the  associative 
and  commissural  neurones  that  relate  them  one  to  the  other. 
On  account  of  this  fact,  all  those  regions  of  the  cerebral  cortex 
not  immediately  connected  with  the  afferent  or  efferent  conduc- 
tion paths  were  named,  by  Paul  Flechsig,  the  association 
centers. 

S3mapses. — Behte  and  others  claim  that  neurones  are  joined 
together  by  fusion  or  "concrescence;"  they  claim  actual  con- 
tinuity of  the  neurones  forming  a  conduction  path.  In  higher 
animals  Heald  has  positively  disproved  this  view  of  Be  the. 
He  shows  that  the  boundaries  of  the  individual  neurones  are 
definite  and  unmistakable  and  do  not  fuse  with  one  another. 
The  relation  is  one  of  contact,  synapsis.  However,  the  complex- 
ity of  the  contacts  varies:  (i)  The  simple  end-brushes  touch  the 
dendrites  or  cell-body  of  the  adjacent  neurone.  (2)  The  telo- 
dendria  are  flattened  and  moss-like  (Cajal),  as  in  cerebellar  cor- 
tex. (3)  The  telodendria  are  shaped  into  cups,  as  the  acustic 
cups  of  the  trapezoid  body.  (4)  Complicated  end-brushes  inter- 
weave with  equally  complex  dendrites,  forming  glomeruli,  as  in 
the  olfactory  bulb.  (5)  "Climbing  fibers,''  the  telodendria  of 
corticipetal  fibers,  entwine  about  the  dendrites  of  the  Purkinje 
cells  in  cerebellar  cortex.  (6)  Pericellular  networks  and  baskets 
are  formed  by  telodendria  about  the  pyramids  of  cerebral  cortex 
and  Purkinje  cells  of  cerebellimi. 

The  white  matter  of  the  cerebro-spinal  axis  is  made  up  chiefly 
of  bundles  of  medullated  axones  imbedded  in  neuroglia  and 
supported  by  connective  tissue.  The  fibers  possess  no  neuri- 
lemma. 

The  gray  matter  of  the  central  nervous  system  is  composed  of 
cell-bodies  and  dendrites,  chiefly,  but  also  contains  axones. 
These  nerve  elements  are  supported  by  connective  tissue  and 
blood-vessels  and  are  imbedded  in  a  great  abundance  of  neu- 
orglia.  The  nerve  fibers  in  the  gray  matter  are  to  a  large 
extent  non-meduUated  and  naked. 

The  cerebral  gray  substance  {substantia  grisea  cerebri)  is  con- 
veniently divided  into  three  groups  or  classes: 
I.  Cortical. 


CEREBRAL   CORTEX 


187 


II.  Nuclear  or  ganglionar. 
III.  Central,  or  ventricular. 


.     .  W  O  CO  p. 


0*3- 


-  "  ■"  S 

V     S  «>  S  rt  V  h 

(u  «  '^  <u  ,  •^s.H 
y  0)  o  >.a  P.O 

X  •s'Sp.1^"' 

^    "  il  CD  >»! 


01  y  P<  r.  5  O4 


ill^S^ 


O    +i   d  C   OJ  4)  SJ 

.   a  (u  <u  0)  M  Q, 


a5    Si. 


*>-?». 


"■^    »»  >»  •»»  .0  <i.  ^"i 
•+3  Jo  «  0.2  5 


I.    THE  CORTICAL  GRAY  MATTER 

The  substantia  corticalis  consists  of  a  thin  envelope,  the  cor- 
tex (or  bark),  which  forms  the  surface  of  the  hemispheres  and 


1 88  THE   CEREBRUM 

incloses  the  white  medulla,  the  centrum  semiovale.  The  cortex 
varies  in  thickness,  3  mm.  being  the  average.  Thickest  on  the 
surface  of  the  gyrus,  it  grows  thinner  to  the  bottom  of  the  sulci. 
In  the  floor  of  the  small  sulci  near  the  frontal  and  occipital  poles 
of  the  cerebral  hemispheres,  the  thickness  is  only  1.5  mm.;  but 
in  the  crown  of  the  paracentral  gyrus  the  cortex  measures  5— 
6  mm.  It  is  said  to  be  slightly  thicker  in  the  left  hemisphere: 
3-43  per  cent,  thicker  in  left  inferior  frontal  gyrus  than  in  right 
(Melius).  According  to  H.  Wagner,  it  has  an  area  of  187,000- 
221,000  sq.  mm.  If  the  average  thickness  is  3  mm.,  the  en- 
tire mass  of  cortex  equals  from  561-663  cc,  a  little  more  than 
half  the  bulk  of  the  cerebrum.  Its  specific  gravity  j is  1033. 
According  to  the  amount  of  blood  present  in  it,  the  cortex  is 
pinkish-  or  yellowish-gray  in  color. 

Various  methods  of  investigation  have  shown  that  the  cortex 
is  divided  into  many  regions  or  centers,  each  having  its  character- 
istic structure  and  specific  function.  These  centers  have  been 
located  by  pathologic  and  experimental  studies  in  man  and  lower 
animals,  by  a  study  of  myehnization  in  children  from  the  fourth 
month  in  utero  to  the  fourth  month  after  birth  (Flechsig),  and 
by  a  careful  microscopic  study  of  sections  of  mature  cortex 
(Campbell,  Cajal,  Bolton,  Vogt,  Mott,  Brodmann,  Griinbaum 
and  Sherrington,  etc.).  G.  Elliot  Smith  recognizes  28  types  of 
cortex  with  the  naked  eye.  Flechsig  distinguishes  36  typical 
regions  by  his  method.  The  "primary  centers,"  Nos.  i  to  10, 
are  medullated  before  birth.  They  include  the  regions  in 
immediate  connection  with  the  afferent  and  efferent  conduction 
paths:  the  common  sensory  and  motor  regions,  and  the  gusta- 
tory, olfactory,  visual  and  auditory.  The  *' intermediate 
centers,"  Nos.  11  to  31,  begin  to  medullate  one  month  after 
birth,  and  the  "final  centers,"  Nos.  32  to  36,  gradually  medul- 
late later,  progressing  certainly  until  the  twentieth  year  and, 
according  to  Kaes,  until  about  the  forty-fifth  year.  The 
"final  centers"  comprise  the  psychic  regions.  Brodmann 
maps  out  43  types  of  cortex;  Alfred  W.  Campbell,  18  types 
(Figs.  74-79)  • 


MOTOR   CENTERS  I 89 

Cortical  or  Cerebral  Localization  (Figs.  74  and  75).— In 
the  following  study  of  the  cerebral  cortex  I  shall  use  very  exten- 
sively the  recent  work  of  Dr.  Alfred  W.  Campbell,  entitled, 
"Histological  Studies  on  the  Localization  of  Cerebral  Function," 
Cambridge,  England.  In  this  epoch-making  work  we  are  shown 
that  certain  cortical  areas  have  a  characteristic  histological 
structure  that  distinguishes  them  from  all  other  areas.  This  will 
be  referred  to  later  under  "cell  and  fiber  lamination  of  the 
cortex,"  but  to  appreciate  this  histological  evidence  of  localiza- 
tion one  should  thoroughly  study  the  above  work. 

Motor  Area  (Figs.  74,  75,  76  and  77). — The  emissive  motor 
area  is  situated  in  the  anterior  wall  of  the  central  sulcus,  in  the 
posterior  one-half  of  the  gyrus  centralis  anterior  and  in  that 
part  of  the  paracentral  lobule  immediately  continuous  with  it. 
This  is  the  center  for  ordinary  voluntary  motion  on  the  opposite 
side  of  the  body.  Axones  from  this  area  descend  to  the  nuclei 
of  all  motor  nerves.  In  lateral  sclerosis  there  is  degeneration 
and  disappearance  of  the  giant  pyramidal  cells  limited  to  this 
motor  area  (Campbell).  It  is  divided  into  four  segments:  the 
head  and  neck,  the  arm,  the  trunk,  and  the  leg,  named  from 
below  upward.  The  first  extends  to  the  inferior  knee  of  the 
sulcus  centralis  (Rolandi),  though  eye  movements  appear  to  be 
represented  in  the  posterior  end  of  the  middle  frontal  gyrus; 
the  arm  area  comprises  the  region  between  the  genu  inferius 
and  the  genu  superius,  the  thumb,  fingers,  wrist,  forearm,  arm 
and  shoulder  movements  being  represented  in  this  ascending 
order;  just  above  the  shoulder  area,  at  the  genu  superius,  is  the 
trunk  area;  and  above  that,  in  the  anterior  central  gyrus  and  in 
the  paracentral  lobule,  in  front  of  the  sulcus  centralis,  is  the 
center  for  leg  movements.  The  representation  in  the  leg  center 
is  inverted,  the  ascending  order  being  hip,  thigh,  leg,  ankle,  toes 
and  great  toe. 

Motor  points  were  first  positively  located  by  G.  Fritsch  and 
E.  Hitzig  in  the  dog's  brain  (1870).  They  located  centers  for 
(i)  the  neck  muscles,  (2)  the  foreleg  extensors  and  adductors, 
(3)  the  flexors  and  rotators  of  the  foreleg,  and  (4)  the  hind-leg 
muscles— all  in  the  sigmoid  gyrus;  and  a  center  (5)  for  the  face 


IQO  THE    CEREBRUM 

muscles  in  the  coronal  gyrus.  I  have  demonstrated  a  trunk 
center  in  the  sigmoid  gyrus,  between  the  foreleg  and  hind-leg 
centers,  stimulation  of  which  causes  flexion  of  the  spine. 

The  psychic  motor  areas,  or  areas  for  educated  movements 
are  located  just  anterior  to  the  above  motor  areas,  in  the  anterior 
central  gyrus  and  in  the  contiguous  ends  of  the  superior,  middle 
and  inferior  frontal  gyri  (Figs.  74  and  75).  These  areas  are 
believed  to  send  their  axones  to  the  emissive  motor  centers  in 
the  cortex.  The  psychic  motor  center  for  the  lower  extremity  is 
probably  located  just  in  front  of  its  emissive  motor  center  in  the 
anterior  central  and  superior  frontal  gyri.  In  the  posterior  end 
of  the  middle  frontal  gyrus  is  the  psychic  motor  center  for  the 
arm,  the  writing  center  of  Gordinier;  and  in  the  inferior  frontal 
gyrus  the  center  for  the  organs  of  voice  and  speech,  hence  the 
motor  speech  center.  In  right-handed  people  these  centers  are 
developed  only  in  the  left  cerebral  hemisphere. 

The  writing  center  was  definitely  located  by  Gordinier  in 
1899  (Amer.  Jour.  Med.  Sciences).  Paul  Broca  located  the 
center  of  articulate  speech  in  186 1.  Pierre  Marie  contends  that 
the  center  of  articulation  is  not  in  the  inferior  frontal  gyrus  but 
is  more  deeply  situated,  possibly  in  the  lentiform  nucleus. 

Common  Sensory  Area  (Figs.  74  and  75). — According  to  Dr. 
Alfred  W.  Campbell  the  receptive  area  of  common  sensation  is 
limited  to  the  posterior  wall  of  the  sulcus  centralis,  including 
the  anterior  one-half  of  the  posterior  central  gyrus  and  that  part 
of  the  paracentral  lobule  which  is  continuous  with  it.  This 
area  undergoes  exclusive  Nissl  degeneration  in  locomotor  ataxia 
(Campbell).  It  is  probably  divided  into  segments  similar  to 
those  of  the  motor  area  (Spiller). 

Psychic  Sensory  Area  (Figs.  74,  75,  76  and  77). — ^A  large  por- 
tion of  the  remainder  of  the  parietal  cortex  probably  constitutes 
a  number  of  centers  for  the  interpretation  of  common  sensory 
impulses,  hence  the  term,  psychic  sensory  area.  Impressions 
of  the  muscular  sense  are  believed  to  be  interpreted  in  the  supra- 
marginal  gyrus  and  the  center  of  stereognosis  is  said  to  be  located 
in  the  superior  parietal  lobule  and  praecuneus.  Perhaps  other 
parts  interpret  tactile  and  temperature  impulses.     The  whole 


ACUSTIC   CENTER 


191 


receptive  and  psychic  area  of  common  sensation  has  been  called 
the  somcBsthetic  area  (Barker),  though  the  application  of  this 
term  might  better  be  limited  to  the  receptive  area. 


o  V  2  c4 
>."  ""o 

-   52  SSI'S  "S 

O    4343  ^  w  CO  m 

O  .2^  ft  o  o  S. 

Hill 

?,  SS^Sftg 
<P   2i  ^  .X  s^^ 

2  SlQa^QS^Q 


^cw5/fc  aw/€r  (Figs.  74  and  76).— The  rec^/^/^'i'^  acustic  cen- 
ter is  located  in  the  transverse  temporal  gyri  and  in  that  part  of 


192  THE    CEREBRUM 

the  superior  temporal  gyrus  which  is  continuous  with  them.  In 
the  adjacent  part  of  the  superior  and  middle  temporal  gyri,  in 
the  left  hemisphere,  is  the  psychic  acustic  center. 

Optic  Center  (Figs.  75  and  77). — In  the  cuneus  and  lingual 
gyrus  is  located  the  receptive  optic  center  for  the  temporal 
half  of  the  same  retina  and  the  nasal  half  of  the  opposite  one; 
perhaps,  also,  for  the  macula  lutea  of  both  sides.  The  re- 
mainder of  the  occipital  lobe  and,  according  to  Mills  and  others, 
the  angular  gyrus,  also,  form  the  psychic  optic  center.  This 
latter  center  is  probably  unilateral  and  developed  only  in  the 
left  hemisphere  of  right-handed  people. 

The  visual  and  acustic  centers  were  located  by  a  host  of  inves- 
tigators inspired  by  the  work  of  Fritsch  and  Hitzig.  Among 
them  were  David  Ferrier,  Monck,  and  others. 

Olfactory  and  Gustatory  Centers  (Figs.  75  and  77).^ — The  uncus 
hippocampi  and  nucleus  amygdalae  form  the  chief  cortical  center 
of  smell;  in  close  association  with  them,  there  are  the  hippo- 
campus, the  dentate  fascia  and  the  callosal  gyri.  The  gusta- 
tory center  formerly  was  thought  to  be  in  the  anterior  end  of  the 
fusiform  gyrus.  Paul  Flechsig  in  his  recent  studies  of  the 
human  brain  locates  taste  in  the  gyrus  cinguli  contiguous  to  the 
splenium  of  the  corpus  callosum  (Fig.  75).  The  olfactory, 
auditory,  visual,  common  sensory  and  motor  areas  are  all  dis- 
tinguished by  a  definite  characteristic  histological  structure 
peculiar  to  each  region  (Campbell) .  Medullation  of  the  fibers  in 
these  cortical  areas  occurs  at  different  times;  and,  according  to 
Flechsig,  in  the  following  order :  olfactory,  tactile  and  muscular 
sense,  visual,  auditory,  and  gustatory. 

In  the  temporal  lobe  Mills  locates  four  other  centers  which 
include  the  pole,  the  inferior  temporal  gyrus  and  a  part  of  the 
middle  temporal  gyrus  (Fig.  76) .  These  are  from  before  back- 
ward :  the  center  of  intonation  at  the  pole,  the  naming  center,  the 
center  of  equilibration,  and  the  center  of  orientation. 

The  naming  center  Mills  locates  in  the  inferior  temporal  gyrus, 
just  anterior  to  the  middle  of  the  infero-lateral  border  of  the 
hemisphere.     I  have  studied  a  case  of  Dr.  Gamble's  in  which  a 


ASSOCIATION   CENTERS 


193 


pistol  wound  of  this  region  was  followed  by  entire  loss  of  ability 
to  name  familiar  objects. 

All  the  above  motor,  som aesthetic  and  special  sense  areas  are 
provided  with  projection  fibers  which  connect  them  with  defi- 
nite muscle  groups  and  surface  regions  and  with  the  organs  of 
special  sense.  Large  parts  of  the  cerebral  cortex  possess  no  pro- 
jection fibers;  they  are  believed  to  be  associative  in  function. 

Association  Centers  of  Flechsig. — Flechsig  describes  three 
association  centers,  the  anterior,  middle,  and  posterior.     Ante- 


CONCRtTt  CONCtPT 

Yic,  76.— Cortical  areas  after  C.  K.  Mills.     Convex  surface  of  cerebral 
hemisphere.     {Brubaker's  Physiology.) 


rior  Association  Center  (Fig.  78).— According  to  Flechsig, 
that  part  of  the  frontal  cortex  which  embraces  region  35  of 
Flechsig  and  is  anterior  to  the  psychic  motor  region  determines 
the  temperament  and  individuality  of  the  person;  and  as  Mills 
declares,  is  the  center  of  inhibition,  self  control,  attention,  con- 
centration, voHtion.  It  is  the  center  of  ''the  abstract  concept'' 
(Fig.  76).  J.  S.  Bolton  says  of  this  association  center  that  "it 
is  the  last  part  of  the  cerebrum  to  be  developed,  and  is  the  first 
to  undergo  dissolution;  it  is  under-developed  in  amentia  of  all 
13 


194 


THE    CEREBRUM 


grades  and  atrophied  in  dementia,  according  to  its  degree." 
*'It  possesses  the  highest  (mental)  function"  (Brain,  Vol.  29). 
The  posterior  association  center  is  composed  of  those  portions  of 
cortex  situated  between  the  sensory  region  of  the  equatorial 
zone  in  front  and  the  visual  cortex  of  the  occipital  lobe  behind 
and  embraces  several  intermediate  regions  of  Flechsig  and  No. 
34  of  the  final  regions.  This  is  an  association  center  of  the 
senses  (Fig.  74) .  To  acquire  knowledge  of  the  external  world  is 
thus  the  function  of  the  posterior  association  center.     Mills  calls 


Fig.  77. — Cortical  areas  after  C.  K.  Mills.     Medial  and  tentorial  surface  of 
cerebral  hemisphere.     {Brubaker's  Physiology.) 


it  the  center  of  "  the  concrete  concept  ^  (Fig.  76) .  It  includes  there 
psychic  areas,  the  common  sensory,  auditory  and  visual. 
Flechsig  regards  the  island  (of  Reil)  and  the  greater  part  of  the 
middle  and  inferior  temporal  gyri,  all  except  the  anterior  ends, 
including  the  final  regions  Nos.  32  and  36  of  Flechsig,  as  the 
middle  association  center  (Figs.  78  and  79).  Lesions  in  it  are 
followed  by  paraphasia,  loss  of  ability  to  name  objects,  etc. 

Destructive  lesions  of  parts  of  the  motor  or  sensory  cortex  cause 
merely  loss  of  certain  motions  and  sensations  represented  by 


LAMINATION  igr 

those  parts,  but  ablation  of  association  centers  disconnects  the 
sensory,  the  psychic  and  the  motor  regions  and  causes  aphasia, 
agraphia,  change  of  temperament,  impairment  of  the  so-called 
moral  and  intellectual  faculties,  etc.  Ablation  of  the  visual 
psychic  center  or  auditory  psychic  center  produces  mind-blind- 
ness m  the  former  and  in  the  latter  mind-deafness. 


Fig.  78. — Functional  areas  of  cerebral  cortex  as  located  on  the  convex  surface 
by  Paul  Flechsig,  according  to  their  order  of  medullation.  i-io  are  primary 
centers,  their  medullation  is  about  complete  at  birth;  first  eight  have  projection 
fibers:  11-31  are  intermediate  centers,  their  medullation  begins  a  month  after 
birth:  32-36  are  the  final  centers  whose  medullation  extends  into  adult  life,  per- 
haps to  the  forty- fifth  year  (Kaes);  these  are  in  the  association  regions. 


Cell  and  Fiber  Lamination  of  the  Cerebral  Cortex.— There 
is  a  type  of  cerebral  cortex  which,  with  small  but  definite  varia- 
tions, prevails  throughout  the  cerebrum,  excepting  in  the  visual 
and  olfactory  regions  (Fig.  80).  Though  Dr.  CampbelFs  divi- 
sion of  the  cortex  into  seven  layers  of  cells  is  complicated,  it  is 
similar  to  Cajal's  description  and  I  think  it  entirely  worthy  of 
general  adoption  and  shall  follow  it  in  this  work.  It  is  to  be 
regretted  that  the  fiber  and  the  cell  layers  have  not  been  more 


196  THE   CEREBRUM 

satisfactorily  correlated,  as  this  would  assist  in  detemining 
function.  Dr.  Alfred  W.  Campbell  gives  the  layers  as  follows : 
First,  the  layer  of  cells : 

1.  The  plexiform  or  molecular  layer. 

2.  The  layer  of  small  pyramids. 

3.  The  layer  of  medium-sized  pyramids. 

4.  The  external  layer  of  large  pyramids. 


Fig.  79. — Functional  areas  of  cerebral  cortex  as  located  by  Paul  Flechsig 
on  medial  surface,  according  to  their  order  of  meduUation,.  Areas  i-io  are  pri- 
mary and  at  least  the  first  eight  have  projection  fibers;  their  meduUation  is  about 
complete  at  birth:  areas  11-31  are  intermediate,  and  are  not  medullated  until 
sometime  after  birth,  beginning  at  one  month;  areas  32-36  are  medullated  much 
later,  extending  into  adult  life  probably  to  the  forty- fifth  year;  these  areas  are  in 
the  association  centers.  Regions  1-8  are  the  motor,  common  sensory  and  special 
sensory  regions. 

5.  The  layer  of  stellate  or  polymorphous  cells. 

6.  The  internal  layer  of  large  pyramids. 

7.  The  layer  of  fusiform  cells. 
Second,  the  fiber  zones: 

1.  The  fiberless  layer,  or  neuroglia  zone. 

2.  The  zonal  layer,  stratum  zonale. 

3.  The  supraradiary  zone. 


LAMINATION 


197 


JE<t 


Fig.  80. — Section  of  superior  parietal  cortex,  somewhat  diagrammatic,  showing 
the  typical  cell-layers  and  fiber-zones. 
I.  Plexiform  layer.  2.  Layer  of  small  pyramids.  3.  Layer  of  medium-sized  pyramids. 
4.  External  layer  of  large  pyramids.  5.  Layer  9f  stellate  cells.  6.  Internal  layer  of  large 
pyramids,  7.  Layer  of  fusiform  cells.  I.  Fiberless  zone.  II.  Stratum  zonale.  ifi. 
Supraradiary  zone.  IV.  a,  Outer  line  of  Baillarger,  b,  inner  line  of  Baillarger.  V.  Radiary 
zone.     VI.  Felt-work  of  Kaes. 


1 98  THE   CEREBRUM 

4.  The  Baillargic  zone,  outer  and  inner  line  of  Baillarger. 

5.  The  radiary  zone. 

6.  The  felt-work  of  Kaes. 

1.  The  plextform  layer  has  next  the  surface  a  fiberless  zone  of 
neuroglia^  on  account  of  which  it  is  often  called  the  neuroglia- 
layer.  Underneath  the  neuroglia  is  a  more  or  less  dense  plexus 
of  nerve  fibers,  constituting  the  stratum  zonale;  and  then  an  area 
of  sparsely  scattered  fibers  that  belongs  to  the  supraradiary 
zone.  Scattered  here  and  there  in  the  zonal  and  supraradiary 
regions  of  the  plexiform  layer  are  small  stellate  cell-bodies^  four 
or  six  microns  in  diameter,  belonging  to  the  types  of  Golgi  and 
Cajal,  whose  dendrites  and  axones  ramify  in  the  stratum  zonale, ' 
some  near  the  cell-body  and  others  at  a  considerable  distance 
from  it.  There  are  also  some  large  horizontal  cells  whose  axones 
run  tangentially  within  the  stratum  zonale.  The  stratum 
zonale  also  contains  dendritic  processes  from  subjacent  laminae, 
the  T-branched  axones  of  Martinotti's  cells,  and,  perhaps,  the 
end-tufts  of  incoming  fibers  from  the  commissural,  the  associa- 
tive and  the  projection  systems.  It  is  very  well  marked  in  the 
motor  area  (Fig.  81),  not  so  well  in  the  common  sensory  area 
(Fig.  82.)  In  the  uncus  it  is  very  distinct  (Fig.  84)  and  is  so 
thick  and  dense  in  the  gyrus  hippocampi  (the  subiculum)  as  to 
be  visible  to  the  naked  eye  (Fig.  85).  The  zonal  layer  of  fibers 
is  faint  in  the  visuo-sensory  and  audito-sensory  cortex.  The 
stratum  zonale  appears  to  grow  richer  with  the  education  of 
the  individual.  The  function  of  the  plexiform  layer  is  commonly 
thought  to  be  association. 

2.  The  layer  of  small  pyramids  (Figs.  80  and  82),  as  well  as 
the  third  layer,  is  situated  in  the  supraradiary  zone.  It  is  com- 
posed chiefly  of  small  closely  packed  cell-bodies,  pyramidal  in 
shape.  They  measure  eight  to  ten  microns  in  diameter.  Their 
apices  point  toward  the  surface.  From  the  apices,  surfaces  and 
lateral  angles,  dendrites  are  given  off  which  ramify  in  the  stratum 
zonale  of  the  first  layer.  The  axone  issues  from  the  base  of  the 
pyramid  and  runs  down  through  the  subjacent  layers.  Among 
the  small  pyramids  are  a  few  polymorphous  cells.  There  are  a 
few  large  and  small-second  type  cells  and  Martinotti  cells. 


MOTOR   CORTEX 


199 


'iMM^:-^:  J      ;ff?'ifffFii!ffMfflii 


Fig.  81. — Cell  and  fiber  lamination  in  the  posterior  half  of  the  anterior  central 
gyrus.  The  motor  area.  (After  A .  W.  Campbell's  "Histological  Studies  on  the 
Localization  of  Cerebral  Function."  Published  by  the  Syndics  of  the  Cambridge 
University  Press.) 

A.  Stained  to  show  only  fibers.  B.  Stained  to  show  only  cell-bodies,  z.  Stratum  zonale. 
s.  Supraradiary  zone.  B.  Line  of  Baillarger.  R.  Radiary  zone  in  the  deep  part  of  which 
is  the  felt-work  of  Kaes.  i.  Plexiform  layer.  2.  Layer  of  small  pyramids.  3.  Layer  of 
medium-sized  pyramids.  4.  External  layer  of  large  pyramids.  5.  Stellate  or  polymor- 
phous cells.    6.  Internal  layer  of  large  pyramids.    7.  Layer  of  fusiform  cells. 


200  THE    CEREBRUM 

The  axones  of  the  small  second -type  cells  form  very  rich  arbori- 
zations which  extend  into  the  stratum  zonale.  The  T-branched 
axones  of  Martinotti's  cells  also  ramify  in  this  stratum  (see 
below) . 

3.  The  layer  of  medium-sized  pyramids  (Fig.  80)  is  a  nearly 
pure  layer;  and,  like  the  overlying  layer,  is  nearly  uniform 
throughout  the  cerebral  cortex.  In  arrangement  of  cell-bodies 
and  processes  it  is  like  the  second  layer.  The  pyramids  get 
farther  apart  and  become  larger  in  size  as  the  layer  is  descended. 
They  measure  ten  to  fifteen  microns  in  their  vertical  diameter. 
Besides  the  pyramids,  there  are  second-type  cells  with  exceed- 
ingly rich  dendritic  and  axonic  processes,  the  double-brush 
cells  of  Cajal,  whose  branches  associate  the  cells  of  the  first  four 
layers  of  cortex.  Basket  cells  are  also  present.  Their  axones 
run  tangentially  and  give  off  collaterals  that  form  pericellular 
baskets  around  the  external  large  pyramids.  The  faint  super- 
radiary  line  (J.  S.  Bolton)  is  at  the  level  of  the  medium-sized 
pyramids.  Layers  " two "  and  ''three"  might  be  combined  in 
one  as  was  formerly  the  custom. 

4.  External  Layer  of  Large  Pyramids  (Figs.  80  and  81). — This 
layer  coincides  in  position  with  the  outer  line  ofBaillarger.  The 
pyramids  are  larger  and  farther  apart  than  in  the  above  layer, 
and  show  a  considerable  accession  of  Nissl  bodies  as  compared 
with  the  smaller  pyramids.  They  measure  15  to  20  ju  by  25  to 
30  M,  and  form  ''one  of  the  most  important  criteria  in  dividing 
the  brain  surface  into  different  histological  territories"  (Camp- 
bell). The  apical  processes  appear  to  reach  the  first  layer  and 
ramify  in  the  stratum  zonale;  the  lateral  and  basal  dendrites 
arborize  within  the  outer  line  of  Baillarger;  the  axone  runs  in- 
ward to  the  white  substance.  The  external  large  pyramids  are 
found  in  nearly  all  parts  of  the  cortex.  Golgi,  <I!ajal  and 
Martinotti  cells  are  intermingled  with  them.  There  are  some 
peculiar  Golgi  cells  among  these  pyramids  whose  axones  run 
horizontally  and  give  off  collaterals  that  form  pericellular  bas- 
kets around  the  pyramids  (Johnston) .  They  are  associative  in 
function.  In  the  motor  cortex,  the  external  large  pyramids 
show  Nissl  degeneration  and  later  complete  destruction  in  amyo- 


CORTICAL   LAYERS  20I 

trophic  lateral  sclerosis.  They  lie  within  the  outer  line  of 
Baillarger.  In  visual  cortex,  along  the  calcarine  fissure,  the 
superficial  large  pyramids  are  replaced  by  large  stellate  cells, 
and  the  double  zone  of  stellate  cells  (fourth  and  fifth  layers) 
incloses  the  very  thick  outer  line  of  Baillarger.  Bolton  locates 
the  inner  line  inferior  to  layer  5.  There  are  two  lines  of  Bail- 
larger  well  shown  in  the  superior  parietal  gyrus  and  in  many 
other  places;  one  in  the  fourth  and  the  other  in  the  sixth  layer. 
The  lines  of  Baillarger  are  very  faint  in  motor  and  common  sen- 
sory cortex. 

5.  The  layer  of  stellate  or  polymorphous  cells  presents  great 
variation  in  different  regions  and  is  a  valuable  guide  for  cortical 
localization.  It  is  a  characteristic  of  all  sensory  cortex  except 
olfactory.  It  is  best  marked  in  the  calcarine  area  (Fig.  83) 
where  it  and  the  fourth  layer  are  associated  with  the  greatly 
thickened  outer  Baillargic  line  (Gennari) .  It  is  well  marked  in 
the  auditory  cortex.  In  the  motor  area  it  is  hardly  distinguish- 
able, but  it  appears  suddenly  at  the  bottom  of  the  central  sulcus 
and  forms  a  distinct  feature  in  the  common  sensory  region  of 
the  posterior  central  gyrus  (Fig.  82).  The  cell-bodies  of  the 
stellate  layer  measure  five  to  eight  microns  in  diameter  and  are 
of  many  shapes,  some  being  pyramidal.  They  are  richly 
branched.  The  dendrites  arborize  at  once  near  the  cell-body. 
The  axones  of  a  considerable  number  of  cells  extend  horizontally 
within  the  layer,  while  others  run  toward  the  surface  and  end  in 
the  overlying  laminae. 

6.  Internal  Layer  of  Large  Pyramids  (Fig.  81). — This  is  the 
most  important  layer  of  the  cortex  for  localization.  It  lies  in 
the  radiary  zone  of  fibers  and  is  present  in  almost  every  part  of 
the  cerebral  cortex,  though  distinguished  by  definite  variations 
in  the  different  regions  (Figs.  82,  83  and  84).  Its  great  pyra- 
mids are  intermingled  with  irregular  cell-bodies  of  the  Golgi 
type  and  with  Martinotti  cells.  They  are  loaded  with  Nissl 
bodies  and  give  off  one  axone  and  many  dendrites.  The  lateral 
and  basal  dendrites  ramify  in  the  inner  line  of  Baillarger;  the 
dendrite  of  the  summit  runs  straight  out  toward  the  surface  and, 
like  the  same  process  from  other  pyramids,  arborizes  in  the 


202  THE   CEREBRUM 

stratum  zonale  of  the  plexiform  layer;  the  axone  enters  the 
medullary  substance  and  becomes  a  projection,  association  or 
commissural  fiber.  The  giant  pyramids  (Betz),  or  ganglionic 
cells  (Bevin Lewis),  of  the  anterior  central  gyrus  are  ^'pyriform'^ 
in  shape.  The  giant  pyramids  characterize  the  motor  cortex. 
Nowhere  else  are  they  so  large.  Neither  do  they  have  in  any 
other  region  the  ''pyriform''  shape  or  the  definite  nest-like 
grouping  seen  in  the  anterior  central  gyrus.  They  measure  25 
by  60  microns  in  the  leg  area  of  that  gyrus;  20  by  45  microns 
in  the  arm  area;  and  in  the  head  area  17  by  35  microns  (Bevin 
Lewis).  In  cases  of  amyotrophic  lateral  sclerosis  studied  by 
Campbell,  87.5  per  cent,  of  these  cells  in  the  affected  area 
were  entirely  destroyed  and  those  remaining  showed  signs 
of  degeneration.  According  to  Holmes  and  May,  the  pyriform 
pyramidal  cells  in  the  sixth  layer  give  entire  origin  to  the  pyra- 
midal tracts  (the  cerebrospinal  fasciculi)  and  their  axones  enter 
no  other  systems  (Brain,  Vol.  32). 

7.  The  fusiform  layer  (Figs.  81,  82,  83  and  84)  is  found  every- 
where in  the  cerebral  cortex.  It  presents  very  little  topograph- 
ical variation.  Its  spindle-shaped  cell-bodies  lie  in  the  deep 
part  of  the  radiary  zone  and  in  the  felt-work  of  Kaes.  The  long 
axes  of  the  spindles  are  perpendicular  to  the  surface  in  the 
crown  of  a  gyrus  but  are  parallel  with  it  in  the  fissural  walls  and 
floor.  From  these  cell-bodies  one  axone  and  several  dendrites 
are  given  off;  the  dendrites  arborize  toward  the  surface,  the 
axones  are  corticifugal.  The  function  of  the  spindle  cell  is 
probably  association.  The  felt-work  of  Kaes  is  a  rich  plexus  of 
fibers  in  which  the  white  and  gray  substance  meet.  It  is  pro- 
duced by  the  intermingling  of  the  association,  commissural  and 
projection  fibers. 

Atypical  Neurones. — We  have  noticed  two  atypical  neurones 
scattered  among  the  typical  cells  of  the  various  layers,  viz. :  (i) 
several  sizes  and  varieties  of  second-type  neurones,  including  the 
double-brush  cells  of  Cajal,  and  (2)  the  inverted  pyramids  of 
Martinotti,  all  associative  in  function.  The  dendrites  of  the 
Martinotti  cells  are  short  and  simple.  The  axones  run  toward 
the  stratum  zonale,  giving  off  collaterals  at  different  levels ;  they 


SENSORY  CORTEX 


203 


r  -~:^ 


H' 


IV-. 


^^-^r'v 


\ 


\:y. 


i 


.  'Si 


■    ••       ■  ..■•-  J 

Fig.  82. — Cell  and  fiber  lamination  in  the  anterior  Jialf  of  the  posterior  central 
gyrus.  The  common  sensory  area.  (After  A.  W.  Campbell's  "Histological 
Studies  on  the  Localization  of  Cerebral  Function."  Published  by  the  Syndics  of 
the  Cambridge  University  Press.) 

A.  Stained  to  show  fibers.  B.  Showing  only  cell-bodies,  z.  Stratum  zonale.  s.  Supra- 
radiary  zone.  B.  Line  of  Baillarger.  R.  Radiary  zone.  i.  Plexiform  layer.  2.  Layer  of 
small  pyramids.  3.  Layer  of  medium-sized  pyramids.  4.  Externallayer  of  large  pyramids. 
S.  Layer  of  stellate  cells.     6.  Internal  layer  of  large  pyramids.     7.  Layer  of  fusiform  cells. 


204  THE   CEREBRUM 

terminate  in  T-like  branches  within  the  plexiform  or  some 
deeper  layer. 

Axones  of  the  Cortex. — There  are  three  systems  of  axones 
in  the  cortex:  the  projection,  the  association  and  the  com- 
missural. The  projection  system  includes  corticifugal  and 
corticipetal  fibers.  The  first  are  axones  of  the  pyramids  in 
the  cortex  which  descend  to  nuclei  at  lower  levels  in  the  cerebro- 
spinal axis,  bearing  impulses  away  from  the  cortex.  The 
second  rise  in  nuclei  of  lower  levels  and  terminate  in  the  cortex; 
they  carry  afferent  impulses  to  the  cortex.  Both  sets  of  axones 
enter  into  the  cortical  radiations  (of  Meynert)  and,  by  their 
collaterals,  help  to  form  the  tangential  fibers  of  the  zonal  and 
Baillargic  lines.  The  association  fibers  of  the  cortex  are  (i) 
the  dendrites  of  the  pyramidal,  stellate  and  fusifom  cells  and 
(2)  the  axones  and  dendrites  of  the  Golgi,  Cajal  and  Marti- 
notti  cells.  These  two  groups  associate  the  different  laminae 
and  the  closely  adjacent  cells  of  the  same  lamina.  They  com- 
prise many  fibers  of  the  stratum  zonale  and  of  the  lines  of 
Baillarger.  (3)  The  axones  of  pyramids  and  fusiform  cells 
that  descend  into  the  white  substance  and  run  to  some  other 
part  of  the  cortex  in  the  same  hemisphere  constitute  the  longer 
association  fibers.  The  commissural  fibers  are  also  axones  of 
the  pyramids  (and  perhaps  of  the  fusiform  cells).  They  pass 
from  the  cortex  of  one  hemisphere  to  that  of  the  other  side. 

Radiations. — The  various  fibers  leaving  and  entering  the 
cortex  are  the  chief  constituents  of  the  cortical  radiations 
(of  Meynert);  the  Martinotti  cells  and  the  apical  dendrites 
of  the  deep  pyramids  and  fusiform  cells  assist  somewhat.  In 
temporal  cortex  where  the  lines  of  Baillarger  are  very  faint  or 
absent  and  the  radiations  very  long,  the  apical  dendrites  of 
nearly  all  the  pyramids  enter  into  the  radiations:  here,  the 
radiary  zone  extends  to  the  stratum  zonale. 

Atypical  Cortex. — The  decided  variations  from  the  typical 
cortex  are  found  in  the  visual  and  olfactory  areas. 

Visual  Receptive  Center  (Fig.  83) . — The  cortex  in  the  cuneus 
and  gyrus  lingualis  presents  three  marked  variations  from  typical 
cortex:  i.  The  greatly  accentuated  outer  line  of  Baillarger, 


OLFACTORY   CORTEX  205 

which  may  be  seen  with  the  naked  eye  dividing  the  cortex 
into  two  gray  layers.  This  line  was  first  seen  and  described 
in  the  visual  area  by  Gennari  (1776)  and,  ten  years  later,  by 
Vicq  d'Azyr.  It  is  present  only  in  the  visuo-sensory  cortex; 
elsewhere,  there  is  a  very  faint  outer  line  Baillarger.  2.  The 
external  layer  of  large  pyramids  is  replaced  by  a  layer  of  stellate 
cells  25;u  in  diameter.  These  stellate  cells  give  off  three  or 
four  strong  processes  which  appear  to  arborize  in  the  outer 
line  of  Baillarger  just  beneath  it.  They  are  found  in  the 
receptive  visual  areas  but  not  elsewhere  in  the  cerebral  cortex. 
Beneath  the  deep  stellate  cells  (layer  5)  is  the  inner  line  of 
Baillarger  (Bolton).  3.  The  internal  layer  of  large  pyramids 
is  replaced  by  a  conglomerate  made  up  of  three  varieties  of 
pyramids.  From  without  inward  there  are:  First,  small  in- 
verted pyramids,  cells  of  Martinotti,  which  extend  their  axones 
out  toward  the  surface.  Second,  the  scattered  giant  pyramids, 
25-30JU  in  diameter,  arranged  in  a  single  row  and  called  the 
solitary  cells  of  Meynert.  The  axones  of  the  giant  pyramids 
probably  pass  into  the  optic  radiation.  Third,  a  layer  of 
medium-sized  pyramids. 

Olfactory  Cortex. — All  the  divisions  of  the  rhinencephalon 
are  here  mentioned,  though  only  a  part  of  them  need  be  de- 
scribed: the  olfactory  bulb,  triangle,  parolfactory  area,  anterior 
perforated  substance,  septum  pellucidum,  gyrus  subcallosus, 
gyrus  supracallosus  (longitudinal  striae),  fasciola  cinerea,  gyrus 
subsplenialis,  fascia  dentata,  hippocampus,  subiculum  and 
uncus.  The  posterior  inferior  part  of  the  hippocampal  gyrus 
and  the  gyrus  cinguli  are  ordinarily  included  in  the  rhinen- 
cephalon; but,  according  to  Elliot  Smith,  they  belong  to  the 
neopallium  (Figs.  84,  85  and  86). 

The  cortex  of  the  olfactory  bulb  (Fig.  86)  is  divided  into  five 
layers  as  pictured  by  Barker.  These  five  layers  are  as  follows, 
named  from  the  surface  toward  the  center:  (i)  The  stratum 
nervosum,  composed  of  the  T-branched  fibers  from  the  olfactory 
nerve  and  their  collaterals.  These  fibers  run  nearly  parallel 
with  the  surface  for  some  distance,  then  bend  centrally  and 
break  up  into  their  end-tufts  in  the  second  layer.     (2)  The 


2o6 


THE   CEREBRUM 


stratum  glomerulosum  is  made  up  of  round  bodies,  called  glom- 
eruli, which  are  composed  of  the  end-tufts  of  olfactory  nerve 
fibers  and  of  brush-like  dendrites  from  the  spindle  and  mitral 
cells  of  the  third  and  fourth  layers.  The  glomeruli  constitute 
the  synapses  between  the  first  and  second  olfactory  neurones. 


Fig.  83. — C  .  .n  the calcarine region.     ]vLci.L'ii\i.  visual 

AREA.  (After  A.  W .  UampbeU's  "Histological  Studies  on  the  Localization  of 
Cerebral  Function."  Published  by  the  Syndics  of  the  Cambridge  University 
Press.) 

A.  Shows  fibers  of  occipital  cortex.  B.  Cells  of  same.  z.  Stratum  zonale.  s.  Supra- 
radiary  zone.  G.  Line  of  Baillarger  or  Gennari,  r.  Radiary  zone,  i.  Plexiform  layer.  2. 
Layer  of  small  pyramids.  3.  Layer  of  medium-sized  pyramids.  4.  External  layer  of 
large  stellate  cells.  5.  Small  stellate  cells.  6.  Layer  of  giant  pyramidal  or  stellate  cells 
with  some  small  pyramids.     7.  Layer  of  fusiform  cells  with  some  medium-sized  pyramids. 


(3)  The  stratum  reticulare.  This  is  a  network  of  mitral  den- 
drites interwoven  with  arborizing  processes  from  the  granules 
in  the  fifth  layer  and  the  branches  of  a  few  endogenous  spindle 
cells,  called  the  brush  cells.  The  mitral  dendrites  are  on  their 
way  to  the  glomeruli  in  the  second  layer.     The  spindle  cells 


VISUAL   CORTEX  207 

likewise,  both  large  and  small,  throw  their  dendritic  processes 
down  into  the  stratum  glomerulosum,  where  they  end  in  rich 
tufts  or  brushes;  and  their  axones  penetrate  the  fourth  and  fifth 
layers,  enter  into  the  white  sheath  of  the  bulb  and  thence  are 
continued  into  the  olfactory  tract.  (4)  The  stratum  cellulare, 
or  layer  of  mitral  cell-bodies.  The  mitral  cells  have  large 
pyramidal  bodies  with  one  axone  and  rich  dendritic  processes. 
The  latter  arborize  through  the  reticular  layer  to  the  glomeruli 
of  the  second  layer,  where  they  terminate  in  the  form  of  end- 
brushes.  The  axones  of  the  mitral  cells  run  centrally  through 
the  granular  layer,  to  which  they  give  off  collaterals,  and  then 
turn  backward  in  the  white  sheath  and  constitute  most  of 
the  olfactory  tract.  The  white  sheath  incloses  a  mass  of  cells 
derived  from  the  ependymal  lining  of  the  ventricle  in  the  em- 
byro.  (5)  The  stratum  granulosum  is  composed  of  a  thick 
layer  of  small  cell-bodies,  "granules,"  whose  processes  arborize 
richly  in  the  granular,  cellular  and  reticular  layers.  Imbedded 
in  the  granular  layer  are  the  meduUated  axones  coursing  toward 
the  white  sheath  and  the  olfactory  tract.  The  function  of  the 
granular  layer  is  not  understood.  The  mitral  and  spindle  cells 
of  the  olfactory  bulb,  it  should  be  carefully  noted,  form  the 
terminal  nucleus  of  the  olfactory  nerves;  the  points  of  contact 
between  them  are  estabHshed  in  the  glomeruli;  and  the  axones 
of  the  nucleus  constitute  the  olfactory  tract  and  terminate  in 
four  nuclei — the  cortex  of  the  olfactory  tract,  the  olfactory 
triangle,  anterior  perforated  substance  and  septum  pellucidum. 
In  these  nuclei  lie  the  bodies  of  the  third  order  olfactory  neu- 
rones, whose  axones  form  the  olfactory  striae:  the  medial,  the 
intermediate  and  the  lateral  olfactory  striae  (Fig.  86).  The 
lateral  stria  of  the  olfactory  tract  runs  directly  to  the  uncus, 
hence  we  shall  study  that  region  next. 

The  uncus  of  the  hippocampal  gyrus  (Figs.  75,  84  and  85) 
probably  represents  the  greater  part  of  the  lobus  pyriformis 
of  osmatic  mammals.  It  constitutes  the  chief  cortical  center 
of  smell.  However,  it  is  probable  that  the  subiculum,  hippo- 
campus, fascia  dentata,  the  subsplenial  and  callosal  gyri  belong 
in  the  cortical  area  of  smell,  as  all  showed  arrested  development 


208 


THE   CEREBRUM 


>    > 


\ 


N^* 


Fig.  84. — Cell  and  fiber  lamination  in  the  uncus  hippocampi  (lobus  pyri- 
formis).  The  area  of  smell.  (After  A.  W.  CampbeWs  "Histological  Studies 
on  the  Localization  of  Cerebral  Function.  Published  by  the  Syndics  of  the 
Cambridge  University  Press.) 


A.  Showing   fibers.     B.  Showing   cell-bodies,     z.  Stratum   zonale,   external    medullary 
Supraradiary 
Radiaryzone.     i.  Plexiform  layer.     2.  Layer  of  stellate  cells  showing  cell-nests.     3.  Repre- 


lamina.     s.  Supraradiary    zone    containing   radiating    fibers.     B.  Line  of    Baillarger. 


sents  third  and  fourth  layers  of  typical  cortex,  medium-sized  pyramids  obliquely  placed  and 
stellate  cells;  with  Golgi's  silver  method  shows  tassel-cells.  4.  Fusiform  or  triangular  cells. 
5.  Medium-pyramids.     6.  Fusiform  cells. 


OLFACTORY   CORTEX  209 

in  two  cases  of  congenital  absence  of  the  olfactory  bulbs 
(Zuckerkandl).  The  fascia  dentata  is  of  first  importance  ac- 
cording to  Alexander  Hill.  He  calls  attention  to  the  fact  that 
the  narwhal,  which  has  no  sense  of  smell,  possesses  every  part 
of  the  hippocampal  region  excepting  the  dentate  fascia  (Camp- 
bell). The  uncus  comprises  the  whole  anterior  part  of  the 
gyrus  hippocampi.  In  structure  the  crown  of  the  hippocampal 
gyrus  and  the  uncus  are  nealy  identical.  They  have  only 
five  layers  of  cells,  (i)  As  already  pointed  out  the  plexiform 
layer  is  thick  and  possesses  a  dense  stratum  zotiale,  only 
second  to  that  of  the  subiculum.  (2)  The  place  of  the  small 
pyramids  is  usurped  by  the  ''olfactory  islets''  (Calleja)  which 
are  curious  nests  of  large  stellate  cells  (28/1)  interspersed  with 
small  nests  of  very  minute  pyramidal  cells.  (3)  The  tassel- 
cells  of  CajaL  Peculiar  pyramidal  cells,  with  such  rich  dendritic 
arborizations  hanging  from  the  bases  as  to  resemble  tassels, 
are  seen  in  the  place  of  the  medium-sized  pyramids.  At  the 
line  of  Baillarger  there  are  no  cells;  the  fourth  layer  of  typical 
cortex  is  entirely  wanting.  (4)  The  stellate  layer  and  internal 
layer. of  large  pyramids  are  replaced  by  a  layer  of  intermixed 
fusiform  and  triangular  cells  heavy  with  Nissl  bodies.  (5) 
The  fusiform-cell  layer  is  nearly  typical. 

Nucleus  AmygdalcB  (Fig.  39). — In  the.  anterior  wall  of  the 
inferior  horn  of  the  lateral  ventricle,  near  the  temporal  pole  and 
dorsal  to,  but  continuous  with,  the  uncus  hippocampi,  is  the 
amygdala,  a  nucleus  of  doubtful  classification.  The  amygdala 
is  in  part  continuous  with  the  corpus  striatum  and,  according 
to  Campbell,  appears  on  the  surface  of  the  uncus  as  the  gyrus 
semilunaris. 

Subiculum  Hippocampi,  the  Lower  Wall  of  Hippocampal 
Sulcus  (Fig.  85). — This  is  known  as  the  subiculum.  It  is 
especially  distinguished  for  its  remarkable  stratum  zonaUy  which 
is  visible  to  the  naked  eye,  and  for  its  long  radiations^  which 
reach  the  zonal  layer  and  give  the  cortex  a  striated  appearance, 
(i)  The  plexiform  layer  is  almost  wholly  occupied  by  the  stratum 
zonale,  called  here  the  external  medullary  lamina.  (2)  The  layer 
of  olfactory  islets.  The  islets  are  closely  packed  nests  of  minute 
14 


2IO 


THE    CEREBEUM 


triangular  cells,  5  m  in  diameter,  resembling  those  in  the  uncus. 
(3)  The  stratum  radiatum  occupies  about  three-fourths  of  the 
depth  of  this  cortex.  In  its  deep  part  (the  stratum  lucidum) 
there  are  several  layers  of  medium-sized  pyramids,  arranged  in 
columns.     The  prominent  apical  processes  of  these  pyramids 


////  / 


Fig.  85. — Transverse  section  of  the  hippocampal  formation.     (After  Edinger.) 
a.   Nucleus  of  fascia  dentata. 

collect  in  bundles  and  proceed  outward  to  the  stratum  zonale, 
separating  the  columns  of  pyramids  and  producing  the  striations 
above  mentioned.  As  the  apical  dendrites  approach  the  olfac- 
tory islets  they  branch  richly.  The  axones  of  the  pyramids  run 
straight  to  the  white  core  of  the  gyrus  or  into  the  alveus.     The 


FASCIA   DENTATA  211 

pyramids  continue  without  interruption  through  the  hippo- 
campus into  the  nucleus  of  the  dentate  fascia.  The  alveus, 
which  forms  the  ventricular  surface  of  the  hippocampus,  is 
made  up  largely  of  the  axones  of  these  pyramids;  from  the 
alveus  they  proceed  into  the  crus  of  the  fornix.  (4)  A  few  fusi- 
form or  stellate  cells  lie  next  the  alveus.  They  belong  to  the 
t3^e  of  Golgi,  the  axone  being  wonderfully  branched.  In 
function  they  are  associative.  It  is  in  the  region  of  these 
associative  neurones  that  the  axones  of  the  pyramids  bend  and 
adjust  themselves  so  as  to  enter  the  alveus  nearly  parallel  with 
its  surface,  hence  the  name  stratum  oriens  applied  to  it  by 
Edinger. 

The  fascia  dentata  (Fig.  85)  is  a  free  lip  of  cortex  facing  inward 
anterior  to  the  hippocampal  sulcus.  It  presents  a  type  of  struc- 
ture, which  is  continued  forward  through  the  pars  transversa 
into  the  reflected  part  of  the  uncus;  and  which  extends  back- 
ward through  the  fasciola  cinerea  and  gyrus  subsplenialis  into 
the  gyrus  supracallosus.  It  is  similar  in  structure  to  the  sub- 
iculum,  the  first  and  the  third  layers  only  present  a  marked  vari- 
ation. The  stratum  zonale  is  not  so  prominent  as  in  the  sub- 
iculum;  and  the  stratum  radiatum  is  entirely  replaced  by  the 
nucleus  fasciae  dentatae.  The  nucleus  is  composed  of  pyramids 
of  polymorphous  and  fusiform  cells  and  their  branches.  Their 
dendrites  radiate  toward  the  stratum  zonale,  their  axones  pro- 
ceed into  the  crus  of  the  fornix.  The  dentate  fascia  is  absent  in 
anosmatic  animals  (A.  Hill)  (Fig.  41). 

Cortex  Tractus  Olfactorii,  Trigonum  Olfactorium,  Gyrus  Suh- 
callosus,  Septum  Pellucidum,  and  Substantia  Perforata  Anterior 
(Figs.  31  and  34). — These  are  the  parts  into  which  run  the 
fibers  of  the  olfactory  tract  and  out  of  which  grow  the  olfactory 
striae.  They  are  more  conspicuous  in  the  embryo  than  in  the 
adult  human  brain.  The  cortex  of  this  whole  region  is  so  retro- 
gressive as  to  require  but  brief  description.  The  plexiform  layer 
may  be  identified.  The  whole  gray  substance  beneath  that  is 
occupied  by  scattered  pyramids  of  medium  size,  separated  by 
strands  of  fibers  belonging  to  the  olfactory  tract  and  striae  and, 
perhaps,  to  the  cingulum. 


212 


THE   CEREBRUM 


The  cortex  of  the  gyrus  cinguli  (Fig.  34)  is  characterized  by  an 
entire  absence  of  large  fibers  and  large  cells,  by  an  oblique  and 
irregular  direction  of  the  pyramids  and  by  a  most  remarkable 
color  affinity  possessed  by  the  deep  cells.  There  are  only  four 
cell  layers,     (i)  The  plexiform  presents  a  faint  stratum  zonale 


Central  core  of 
ependymal  cells 


5.  S.  granulosum 


4.  S.  cellulare 
3.  S.  reticulare 


2.  S.  glomeru- 
losum 

I.  S.  nervosum 


Nasal  mucous 
membrane 


Olfactory  cell- 
bodies 


Fig.  86, — Chief  elements  of  the  olfactory  bulb.     (Gordinier  after  Van  Gehuchten.) 


but  nothing  characteristic.  (2)  The  layer  of  small  pyramids 
is  ill  defined.  (3)  A  layer  of  medium-sized  pyramids  placed  at 
various  angles  occupies  the  place  of  the  third,  fourth,  fifth  and 
sixth  layers  of  typical  cortex.  (4)  The  layer  of  spindle  cells. 
In  the  spindle-cell  layer  are  found  the  remarkable  chromophilous 
cells.     They  are  triangular  or  pyramidal  in  shape  and  have 


HISTOGENESIS    OF    CEREBRAL   CORTEX  213 

greater  affinity  for  stains  than  the  cells  of  any  other  part  of  the 
cerebral  cortex. 

The  claustrum  (Figs.  38  and  54)  is  a  sheet  of  peculiar  gray 
substance  which,  according  to  Meynert,  may  be  classed  as 
cortical.  In  structure  it  resembles  the  seventh  layer  of  typical 
cortex,  being  made  up  of  fusiform  cell-bodies.  The  claustrum 
is  a  vertical  antero-posterior  sheet  placed  medial  to  the  island, 
and  lateral  to  the  external  capsule.  The  surface  in  contact 
with  the  external  capsule  is  smooth,  but  the  external  surface  is 
convoluted  to  coincide  with  the  gyri  insulae.  At  its  lower 
border  it  joins  the  lentiform  nucleus  and  anterior  perforated 
substance. 

The  histogenesis  of  the  cerebral  cortex  is  not  entirely  clear. 
It  develops  from  within  outward.  It  evolves  earliest  in  the 
anterior  and  posterior  central  gyri,  the  motor  and  sensory  areas. 
Its  development  in  the  special  sense  regions  follows,  being  later 
in  the  psychic  sensory  than  in  the  receptive  sensory;  while  in 
the  prefrontal  region  (higher  psychic)  the  cortex  is  differentiated 
last  of  all. 

The  laminae  are  laid  down  in  the  central  gyri  in  the  18  weeks' 
foetus  studied  by  J.  S.  Bolton;  but  all  neurones  are  embryonic 
except  the  Betz-cells.  Laminae  may  also  be  seen,  with  some 
difficulty,  in  the  anterior  part  of  the  visuo-sensory  cortex, 
where  the  outer  line  of  Baillarger  (line  of  Gennari)  divides  the 
cortex  into  two  zones  of  very  embryonic  cells.  At  the  same 
time  (18  weeks)  the  prefrontal  region  (higher  psychic)  is  crowded 
with  undeveloped  neuroblasts  diffusely  arranged ;  no  lamination 
is  evident  there  until  the  sixth  month  and  the  cortex  is  one- 
half  the  normal  thickness  (Brain,  Vol.  35). 

According  to  J.  S.  Bolton  the  cortex  evolves  in  three  primary  cell-layers; 
an  inner,  a  middle  and  an  outer  and  two  fiber  layers;  an  inner  fiber  layer 
separating  the  inner  and  middle  cell-layers,  and  an  outer  fiber  layer,  the 
stratum  zonale  which  lies  next  the  surface  (Brain,  Vol.  ss). 

The  inner  cell-layer  of  Bolton,  which  corresponds  to  the  fusiform  cells 
and  the  internal  pyramids  of  Campbell  and  Cajal,  is  the  first  to  differen- 
tiate; and  within  it  the  neuroblasts  first  attain  their  full  size  and  form.  It 
is  said  to  be  the  best  developed  cortical  lamina  in  all  mammals  (G.  A. 
Watson).    It  is  thicker  in  the  association  areas  than  in  the  receptive 


214  THE    CEREBEUM 

regions.  Its  thickness  is  equal  in  man  and  the  rhesus  monkey;  but  it  is 
thicker  in  the  dog  than  in  man.  In  the  central  gyriof  the  i8  weeks'  foetus 
of  Bolton,  it  is  faintly  indicated  and  the  Betz-cells  are  the  only  ones  out  of 
the  embryonic  stage.  The  inner  cell-lamina  is  the  fundamental  layer.  By 
inference  it  presides  over  the  organic  and  instinctive  activities. 

The  inner  line  of  Baillarger,  a  microscopic  plexus  of  tangential  fibers, 
may  be  descried  just  above  the  inner  cell-layer  at  the  sixth  month.  The 
line  is  well  developed  only  in  the  association  areas  and  does  not  become 
definite  until  the  seventh  or  eighth  month.  It  occupies  the  level  of  the 
internal  large  pyramids  of  Campbell.  Among  its  fibers  lie  the  giant  pyri- 
form  pyramidal  cells  of  Betz  in  the  motor  cortex  and  the  great  pyramids  of 
Meynert  in  the  visuo-sensory  cortex.  The  Betz-cells  are  present  as  large 
irregular  pyramids  in  the  i8  weeks'  foetus  and  very  clearly  map  out  the 
motor  cortex.  They  measure  at  this  time  29-36/1  in  height  and  7/1  in 
width;  their  nuclei  are  5.5  //in  diameter.  The  Betz-cells  give  rise  to  the 
pyramidal  tract.  They  are  purely  motor.  The  inner  line  of  Baillarger 
appears  to  form  a  part  of  the  instinctive  mechanism  belonging  chiefly  to 
the  inner  cell-layer  (fusiform  cells  and  internal  large  pyramids) . 

The  middle  cell-layer  of  Bolton  is  the  stellate  layer  of  Campbell  (layer 
V).  It  is  represented  only  by  a  few  scattered  cells  in  the  anterior  central 
gyrus;  but  in  all  sensory  cortex,  except  the  olfactory,  it  is  a  prominent 
lamina.  In  the  visuo-sensory  cortex  it  is  exceptionally  developed.  In  that 
it  is  divided  into  two  laminae  at  the  eighteenth  week  by  the  outer  line  of 
Baillarger  (line  of  Gennari);  though  at  that  time  all  its  cells  are  very 
embryonic  and  diffuse  in  arrangement.  It  is  thicker  in  the  visuo-sensory 
than  in  the  visuo-psychic  area  and  is  very  poorly  developed  in  those  blind 
from  birth.  In  the  prefrontal  area  it  varies  in  thickness  inversely  with  the 
degree  of  amentia  and  dementia.  It  is  very  well  developed  in  the  sensory 
projection  areas  of  all  vertebrates.  Constituting  the  receptive  lamina  of 
the  cortex,  its  function  seems  to  be  the  transformation  of  afferent  impulses. 
The  optic  radiation  enters  the  stellate  layer  in  the  visuo-sensory  cortex  and 
forms  the  greater  part  of  the  outer  line  of  Baillarger,  the  line  of  Gennari, 
which  is  a  prominent  naked  eye  feature  in  that  region.  Outside  the  visual 
cortex  there  is  but  one  layer  of  stellate  cells  and  the  outer  line  of  Baillarger 
is  microscopic  and  very  faint,  except  in  association  regions;  it  lies  at  the 
level  of  the  large  external  pyramids. 

The  outer  cell-layer  of  Bolton  embraces  the  small,  medium  and  external 
large  pyramids  of  Campbell.  It  is  poorly  developed  in  all  mammals  below 
man;  it  thickens  and  increases  in  differentiation  with  the  ascent  of  the 
mammalian  scale,  and  is  the  last  layer  evolved  in  man.  At  birth  it  pos- 
sesses only  half  its  normal  thickness  and  its  cells  are  largely  embryonic. 
It  is  one-fourth  thicker  than  all  the  underlying  laminae  in  adult  man;  it 
just  equals  them  in  the  rhesus  monkey,  and  is  but  one-third  as  thick  as  the 


VISCERAL   AND   SOMATIC   AREAS  215 

subjacent  layers  in  the  dog.  Its  thickness  varies  inversely  with  the  degree 
of  amentia  and  dementia;  the  subevolution  and  degeneration  reverse  the 
order  of  development :  when  the  defect  or  the  degeneration  is  only  slight  it 
affects  the  small  pyramids;  then,  the  medium  pyramids,  if  more  severe; 
and,  finally,  the  large  pyramids  in  the  deep  part  of  the  layer.  The  outer 
cell-layer  shows  marked  progressive  improvement  in  the  development  of 
the  individual  pyramids  as  we  pass  from  dog  to  rhesus  and  from  rhesus  to 
man.  The  deeper  pyramids  differentiate  first.  Gradually,  through  a  period 
of  years,  the  evolution  approaches  the  surface.  The  small  closely  packed 
embryonic  neuroblasts  become  arranged  into  irregular  columns  about  the 
eighteenth  week  in  the  motor  and  common  sensory  zones,  elsewhere 
this  occurs  later;  the  cytoplasm  increases  in  bulk  and  develops  its  charac- 
teristic constituents;  the  dendrites  multiply  and  extend  their  arboriza- 
tions; the  pyramidal  form  is  gradually  assumed,  and  the  cells  recede  from 
each  other  as  the  cortex  expands  and  folds  itself  into  gyri.  The  outer 
cell-layer  in  depth  and  differentiation  characterizes  man;  it  is  associative 
and  psychic  in  function. 

Whether  the  cortical  cells  are  developed  in  situ  or  migrate  from  the 
matrix  near  the  ventricle  to  their  adult  position,  is  not  yet  determined; 
E.  Lindon  Melius  presents  evidence  in  support  of  the  migration  theory. 
This  is  also  supported  by  the  analogous  development  in  the  spinal  cord. 
It  has  been  claimed  by  Streeter  and  others  that  there  is  no  migration  after 
four  and  a  half  months;  but  the  findings  of  Melius  show  the  corona  radiata 
filled  with  neuroblasts  in  the  last  two  months  of  pregnancy  and  in  the  early 
extra-uterine  life.  He  concludes  that  the  cortical  neurones  do  not  arise  in 
situ.  They  originate  in  the  matrix  and  continue  to  form  there  and  migrate 
to  their  positions  in  the  cortex  until  a  short  time  after  birth,  when  the 
matrix  is  exhausted.  Not  all  cortical  cells  are  in  position  at  birth.  Melius 
estimates  the  number  of  neurones  ultimately  located  in  the  cortex  at 
100,000  per  cu.  mm.  (Am.  Jour.  Anat.,  Vol.  14). 

Visceral,  Somatic  and  Association  Areas. — In  the  lower  fishes  (ganoids 
and  teleosts)  the  telencephalon  is  little  more  than  olfactory  bulb  and  nucleus 
of  the  terminal  nerve;  the  division  into  hemispheres  is  merely  indicated 
The  lateral  evagination,  which  forms  the  hemisphere,  becomes  progress- 
ively more  complete  in  amphibians,  in  reptiles  and  in  mammals.  In 
man  the  telencephalon  medium  is  very  small,  bounding  the  aula  of  the  third 
ventricle,  while  the  hemisphere  is  ponderous  in  comparison.  The  fore- 
brain,  from  the  lowest  forms  to  the  highest,  is  differentiated  into  visceral 
and  somatic  areas  (J.  B.  Johnston). 

The  visceral  area  is  made  up  of  the  olfactory,  gustatory  and  general 
visceral  centers.  It  receives  the  second  and  third  order  neurones  from  the 
olfactory  bulb  and  the  tractus  pallii  from  the  hypothalamus;  and  it 
possesses  certain  commissures,  the  fornix  and  a  characteristic  structure. 


2l6  THE   CEREBRUM 

Its  parts  develop  rich  associations  with  one  another  and  then  are  cor- 
related with  the  visual  center  and  the  motor  mechanism  employed  to 
obtain  food.  The  visceral  cortex  is  in  this  manner  elaborated  into  a 
large  annular  gyrus,  the  hippocampal  formation  (formerly  called  the  archi- 
pallium).  It  is  large  in  reptiles,  forming,  with  the  medial  and  lateral 
olfactory  gyri,  a  complete  ring;  but  in  mammals  the  development  of 
the  corpus  callosum  destroys  the  superior  part,  leaving  only  the  rem- 
nants— subcallosal  and  supracallosal  gyri — in  that  region.  According  to 
J.  B.Johnston  the  hippocampal  formation  is  of  the  same  age  as  the  somatic 
area;  hence,  it,  may  be  called  rhinopallium  but  not  archipallium. 

The  somatic  area  of  the  fore-brain  is  made  up  of  the  centers  of  cutaneous 
and  muscular  sensibility,  and  the  visual,  static  and  acustic  centers.  It 
receives  the  nervus  terminalis  and  the  thalamo-cortical  fibers,  bearing 
common  sensory  impulses;  also,  the  fibers  ©f  the  visual,  vestibular  and 
cochlear  paths.  Many  automatic  centers  located  primarily  in  the  thala- 
mus and  striatum  are  shifted  during  development  to  the  cortex,  the  func- 
tions of  the  lower  centers  thereby  being  reduced.  The  various  cortical 
centers  enlarge  by  growth  and  internal  association.  They  become  cor- 
related one  with  another,  and  the  somatic  with  the  visceral  centers. 
As  a  result,  certain  correlation  centers  are  formed  between  the  somatic 
and  visceral  centers  which  correspond  to  the  association  areas  of  Flechsig. 
These  correlation  centers  form  common  clearing  houses  where  afferent 
impulses  are  received  upon  an  equality  and  interact  upon  one  another, 
modifying,  annulling  and  combining  them  into  new  forms.  Hence, 
the  response  to  stimuli  in  vertebrates  is  modified  and  rationalized;  it  is 
not  a  simple  reflex  (J.  B.  Johnston,  Anat.  Rec,  Vol.  4). 

The  aggregation  of  the  centers  of  countless  reflex  mechanisms,  together 
with  their  elaboration  and  internal  association,  constitutes  the  sensory 
and  the  motor  cortex,  and  the  correlation  mechanisms  make  up  the 
psychic-sensory,  the  psychic-motor  and  the  higher  psychic  cortex. 

n.  NUCLEAR  OR  GANGLIONAR  GRAY  MATTER 

The  substantia  grisea  ganglionaris  is  found  in  the  basal  gan- 
glia which,  in  their  situation  and  relations,  have  already  been 
considered.  They  should  be  re-studied  in  this  connection. 
They  are  as  follows: 

1 .  In  the  hemisphere : 

The  corpus  striatum,  composed  of  the  caudate  and  the 
lentiform  nucleus. 

2.  In  the  inter-brain: 

The  thalamus,  lateral  and  medial  geniculate  bodies,  nu- 
cleus hypothalamicus  (Luvsi)  and  red  nucleus. 


CORPUS    STRIATUM 


217 


In  the  mid-brain : 

The  superior  and  inferior  quadrigeminal  coUiculi,  the  sub- 
stantia nigra,  and  the  nucleus  lateralis  superior  in  the 
tegmentum. 


Fig.  87. — Horizontal  section  of  cerebrum  through  genu  and  below  splenium 
of  corpus  callosum.  Fornix  and  chorioid  tela  turned  back,  to  show  inter-brain 
and  third  ventricle.     {Original.) 

a.  Head  of  caudate  nucleus,  b.  Stria  medullaris  thalami  (or  pineal  stria),  c.  Chorioid 
groove,  d.  Trigonum  habenulae.  e.  Pineal  body.  f.  Tail  of  caudate  nucleus,  g. 
Tapetum.  h.  Occipito-thalamic  radiation,  i.  Inferior  longitudinal  fasciculus,  j.  An- 
terior horn  of  lateral  ventricle,  k.  Columna  of  fornix.  1.  Recessus  triangularis,  m. 
Anterior  commissure,  n.  Massa  intermedia  (or  middle  commissure),  o.  Posterior  com- 
missure,    p.  Superior  quadrigeminal  coUiculus.     q.  Posterior  horn  of  lateral  ventricle. 

The  corpus  striatum  (Figs.  38,  41  and  89)  is  an  ovoid  mass  of 
reddish-gray  matter  containing  pigmented  multipolar  cell- 
bodies  of  small  size,  the  larger  ones  being  in  the  globus  pallidus. 
Many  of  them  are  spindle  shaped,  some  are  spherical  and  a  few 


2l8  THE    CEEEBRUM 

are  stellate.  The  nuclei  are  relatively  large  and  the  cytoplasm 
is  scanty  and  loaded  with  pigment  in  the  nucleus  caudatus  and 
putamen.  The  dendritic  processes  of  these  neurones  are  rich; 
the  axones  are  short  and  of  small  diameter.  The  internuncial 
axones,  which  associate  one  nucleus  with  another  in  the  striate 
body,  are  very  fine  and  delicate;  the  strio-fugal  axones  are  of 
medium  size,  but  are  much  finer  than  the  adjacent  cerebro- 
spinal fibers  in  the  internal  capsule. 

According  to  Kinnier  Wilson  the  corpus  striatum  has  no 
direct  connection  with  the  cerebral  cortex.  It  is  an  independ- 
ent, autonomous  organ  which  exercises  a  steadying  effect  upon 
the  lower  motor  neurones,  preventing  hypertonicity,  rigidity 
and  tremor.  Its  neurones  are  either  internuncial  or  strio-fugal. 
Many  afferent  and  efferent  fibers  pass  through  the  corpus  stria- 
tum, as  parts  of  the  internal  capsule;  but  the  fibers  that  have 
genetic  or  terminal  relations  to  the  striate  body  form  three 
groups:  I .  The  internuncial  fibers  both  rise  and  terminate  in  it; 
2.  the  strio-fugal  fishers  rise  in  the  globus  pallidus  and  end  in  some 
nucleus  at  a  lower  level;  and  3.  the  strio-petal  fibers  rise  in  infe- 
rior nuclei  and  terminate  in  the  globus  pallidus  and  nucleus 
caudatus. 

1.  Many  delicate  internuncial  axones  link  the  caudatus  with 
the  putamen  and  the  putamen  with  the  globus  pallidus,  a 
smaller  number  of  axones  running  in  the  reverse  direction  join 
the  putamen  to  the  caudatus. 

2.  The  strio-fugal  fibers  rise  in  the  globus  pallidus  and 
descend  in  four  fasciculi :  The  strio-thalamic  fasciculus  contains 
a  few  fibers  from  the  caudatus  in  addition  to  those  from  the  me- 
dial and  lateral  zones  of  the  globus  pallidus;  it  runs  medially, 
piercing  the  superior  lamina  of  the  internal  capsule,  and  ends  in 
the  lateral  nucleus  and  medial  nucleus  of  the  thalamus.  Some 
of  the  fibers  of  the  strio-thalamic  bundle  traverse  the  inferior 
lamina  of  the  internal  capsule  within  the  ansa  lenticularis.  The 
strio-rubral  fasciculus  has  the  same  origin  in  the  globus  pallidus 
as  the  strio-thalamic  bundle  and  its  fibers  are  of  the  same  me- 
dium caliber.  It  ends  in  the  nucleus  ruber.  These  two  fasciculi 
are   dorsal   to   the  strio-hypothalamic  fasciculus;  and   this,   in 


STRIO-PETAL   FIBERS 


219 


turn,  is  dorsal  to  the  strio-nigral  fasciculus.  The  tracts  to  the 
hypothalamic  nucleus  and  substantia  nigra  are  made  up  of  fine 
fibers,  which  issue  from  the  base  of  the  globus  pallidus  through 
the  medullary  laminae;  they  run  through  the  ansa  lenticularis 
in  the  inferior  lamina  of  the  internal  capsule  to  their  destination 


Fig.  88. — Dissection  of  brain  to  show  geniculate  bodies,  optic  tract,  nucleus 
amygdalae,  etc.     (After  Morris's  Anatomy.) 


in  the  nuclei.     The  strio-nigral  fasciculi^s  has  been  called  the 
intermediate  bundle  of  the  basis  pedunculi. 

3.  The  strio-petal  fibers  received  from  below  by  the  corpus 
striatum  may  be  designated  the  thalamostriate  and  hypothalamo- 
striate  fasciculi.  The  thalamo-striate  fibers  connect  the  thala- 
mus chiefly  to  the  nucleus  caudatus,  but  partly  to  the  globus 
pallidus.     The  hypoth  alamo -striate  fasciculus  ends  wholly  in 


220  THE   CEEEBRUM 

the  globus  pallidus;  it  rises  in  the  nucleus  h3^othalamicus  and 
in  other  lower  lying  nuclei.  Probably  it  contains  fibers  of  the 
medial  fillet  and  the  spino-thalamic  tract. 

Lesions  of  the  corpus  striatum  affect  the  internal  capsule,  which 
impales  it;  and  may  cause,  if  extensive,  hemiplegia  and  partial 
hemianesthesia  of  the  opposite  side  of  the  body,  deafness  in 
the  opposite  ear  and  hemianopia  due  to  cortical  isolation  of  the 
corresponding  halves  of  both  retinae. 

The  thalamus  (Figs.  50,  87  and  88)  should  be  restudied  on 
p.  136.  It  was  pointed  out  by  Burdach  that  the  thalamus 
is  composed  of  two  great  parts ^  a  medial  and  a  lateral;  and  this 
fact  is  further  emphasized  by  the  recent  studies  of  Ernest  Sachs 
and  others.  The  medial  part  includes  the  anterior,  medial  and 
habenular  nuclei;  the  two  former  are  closely  linked  to  the  cau- 
date nucleus  and  all  three  are  connected  with  the  sense  of  smell. 
The  lateral  part  of  the  thalamus  embraces  the  lateral;  arcuate 
and  central  nuclei  and  the  nucleus  of  the  pulvinar;  it  receives 
the  common  sensory  and  taste  paths  and  a  part  of  the  visual 
path,  and  is  connected  with  the  globus  pallidus  and  cerebral 
cortex  (Brain,  Vol.  32).  According  to  Head  and  Holmes  the 
thalamus  is  more  than  a  relay  in  the  common  and  special  sensory 
paths.  It  is  also  an  organ  of  consciousness  for  impulses  of  pain, 
temperature  and  state  of  being,  and  a  part  of  the  mechanism 
through  which  the  cerebral  cortex  exercises  an  inhibitory  con- 
trol over  afferent  impulses.  Hence,  cortical  lesions  never  abolish 
sensations  of  pain  and  temperature  and  cortical  isolation  of  the 
thalamus  is  accompanied  by  greatly  exaggerated  response  to 
painful  stimuli  (Brain,  Vol.  34). 

The  thalamus  is  made  up  of  six  definite  nuclei,  of  the  internal 
medullary  lamina  separating  them,  the  stratum  zonale  forming 
its  superior  and  medial  surfaces,  and  another  sheet  of  meduUated 
fibers,  the  zona  lateralis,  forming  its  lateral  surface.  The  nuclei 
are  the  anterior,  medial,  habenular,  arcuate,  central  (centrum 
medianum),  the  lateral  and  the  nucleus  of  the  pulvinar,  which 
is  a  posterior  prolongation  of  the  lateral  nucleus.  The  internal 
medullary  lamina,  which  intervenes  between  the  nuclei,  is  a 
curved  sagittal  sheet  of  fibers,  regular  and  convex  on  its  lateral 


STRUCTURE   OF   THALAMUS  221 

surface;  it  separates  the  lateral  nucleus  from  the  other  nuclei 
and,  by  three  lamellar  branches  extending  toward  the  median 
plane,  it  separates  the  remaining  nuclei  from  each  other.  The 
lamellae  vary  in  different  regions.  There  are  two  main  lamellae, 
a  superior  and  an  inferior,  the  inferior  divides  into  two  in  its 
posterior  part.  The  undivided  vertical  internal  lamina  sepa- 
rates the  anterior  and  lateral  nuclei  in  front.  Farther  back- 
ward, at  the  transverse  plane  cutting  the  anterior  edge  of  the 
mammillary  bodies,  the  medial  nucleus  appears  just  below  the 
anterior  nucleus  and  the  superior  lamella  separates  them.  The 
lamina  here  has  a  Y-form.  The  inferior  lamella  is  first  seen 
between  the  medial  and  arcuate  nuclei  in  the  frontal  plane 
cutting  the  anterior  part  of  the  red  nuclei;  this  lamella  trends 
ventro -medially.  Before  the  section  cutting  the  largest  part 
of  the  red  nucleus  is  reached,  this  inferior  lamella  delaminates 
to  inclose  the  central  nucleus  (centrum  medianum).  Now, 
four  nuclei  appear  one  above  the  other  separated  by  three 
lamellae:  the  arcuate,  central,  medial  and  a  very  thin  zone  of 
the  anterior  nucleus  at  the  top.  As  the  sectioning  proceeds 
backward,  the  anterior  and  arcuate  nuclei  first  disappear,  then 
the  medial  nucleus  and,  finally,  the  central  and  red  nuclei  drop 
out  together  in  sections  through  the  pulvinar.  The  nucleus  of 
the  pulvinar  is  directly  continuous  with  the  lateral  nucleus; 
but,  as  it  has  a  special  function,  it  is  convenient  to  give  it  a 
separate  name. 

The  several  nuclei  contain  small  and  medium -sized  multi- 
polar neurones,  the  larger  neurone-bodies  being  in  the  lateral 
nucleus.  From  the  lateral  nucleus  some  thalamocortical  and 
thalamo-fugal  axones  originate  which  are  of  large  caliber;  all 
other  thalamic  axones  are  small  or  medium  in  size. 

I.  The  nucleus  of  the  anterior  tubercle  (Fig,  56)  receives  the 
fasciculus  mammillo-thalamicus  (Vicq  d'Azyri)  from  the  corpus 
mammillare  and  is  thus  connected  with  the  columna  of  the  for- 
nix and  it  also  receives  olfactory  fibers  from  the  anterior  per- 
forated substance  (Fig.  52).  The  anterior  nucleus  contains 
two  sets  of  neurones,  the  thalamo-caudate  and  the  internuncial, 
whose  axones  are  very  delicate.     There  are  very  many  thalamo- 


222  THE    CEREBRUM 

caudate  axones;  they  end  in  the  caudate  nucleus,  losing  their 
medullary  sheaths  as  they  enter  it.  The  internuncial  axones 
are  few  in  number;  they  connect  the  anterior  nucleus  with  the 
outer  part  of  the  medial  nucleus.  As  no  fibers  are  found  having 
any  other  destination,  the  anterior  nucleus  is  intermediate  be- 
tween the  mammillary  body  and  the  caudate  nucleus. 

2.  The  medial  nucleus  is  joined  to  the  opposite  medial  nu- 
cleus by  the  massa  intermedia  and  is  continuous  with  the 
hypothalamic  gray  matter  in  the  wall  and  floor  of  the  third 
ventricle;  but  the  internal  medullary  lamina  with  its  superior 
and  inferior  lamellae  separates  it  from  the  other  nuclei  of  the 
same  thalamus.  The  medial  nucleus  possesses  thalamo-caudate 
and  internuncial  neurones.  The  cell-bodies  are  small  and  the 
axones  are  fine.  The  thalamo-caudate  fibers  ascend  in  the  lamina 
medullaris  interna  and  break  up  into  fine  branches  which  end 
in  the  caudate  nucleus.  Some  internuncial  fibers  pursue  the 
same  course  and  terminate  in  the  dorsal  part  of  the  lateral  nu- 
cleus; a  few  run  toward  the  massa  intermedia,  but  not  through  it; 
and  a  number  run  ventro-laterally  to  the  central  nucleus.  The 
medial  nucleus  receives  fibers  from  both  brachia  conjunctiva. 

3.  The  nucleus  of  the  habenula  belongs  to  the  epithalamus 
(Fig.  87).  It  lies  beneath  the  trigonum  habenulae.  It  receives 
fibers  from  the  rhinencephalon  through  the  medullary  stria  of 
the  thalamus,  and  originates  a  bundle  of  fibers,  the  fasciculus 
habenulo-peduncularis  or  retroflexus  (Meynerti),  which  may 
be  traced  back  through  the  tegmentum  to  the  interpeduncular 
nucleus  in  the  substantia  nigra.  Beyond  this,  connections 
are  probably  established  with  the  motor  nuclei  of  cerebral 
nerves. 

4.  The  arcuate  nucleus  (semilunar  nucleus)  is  a  small  crescent 
of  gray  substance  in  the  ventral  part  of  the  thalamus,  just  medial 
to  the  main  internal  medullary  lamina.  The  inferior  lamella  of 
that  lamina  separates  it  from  the  outer  half  of  the  inferior  sur- 
face of  the  medial  nucleus,  in  a  frontal  section  through  the  ante- 
rior part  of  the  red  nucleus;  but,  farther  backward,  the  central 
nucleus  develops  in  that  inferior  lamella,  delaminating  it  and 
further  separating  the  arcuate  from  the  medial  nucleus.     Pos- 


NUCLEI   OF   THALAMUS  223 

teriorly,  the  arcuate  nucleus  ends  slightly  before  the  central  and 
red  nuclei. 

5.  The  central  nucleus  {centrum  medianum  Luysi)  lies  be- 
tween the  arcuate  and  medial  nuclei  and  is  intermediate  in  size, 
srnaller  than  the  medial  but  larger  than  the  arcuate  nucleus. 
It  extends  backward  beyond  the  limit  of  the  medial  nucleus, 
into  the  sections  through  the  pulvinar. 

The  arcuate  and  central  nuclei  contain  only  internuncial 
neurones  and  yet  the  cell-bodies  and  axones  are  of  medium  size. 
The  axones  terminate  almost  wholly  in  the  lateral  nucleus;  but 
the  arcuate  nucleus  associates  all  thalamic  nuclei  except  the 
anterior,  and  the  central  connects  all  except  the  anterior  and 
medial  nuclei.  Rubro-thalamic  fibers  and  fibers  of  the  brach- 
ium  conjunctivum  terminate  in  the  central  nucleus  and,  prob- 
ably, other  afferent  fibers  end  in  these  nuclei. 

6.  The  lateral  nucleus  is  the  largest.  It  extends  from  supe- 
rior to  inferior  surface  the  entire  length  of  the  thalamus.  It  also 
fuses  with  the  nucleus  of  the  pulvinar.  It  forms  the  terminal 
nucleus  for  the  larger  part  of  the  tegmental  fibers,  especially 
of  the  medial  fillet,  the  spino-thalamic  tract,  the  gustatory 
tract,  a  part  of  the  medial  longitudinal  bundle,  the  rubro- 
thalamic fibers  and  fibers  of  the  brachium  conjunctivum  of  the 
cerebellum;  and  it  constitutes  the  nucleus  of  origin  for  most  of 
the  fibers  of  the  cortical  fillet.  The  lateral  nucleus  also  receives 
cortico-thalamic  fibers  from  nearly  every  projection  area  of  the 
cerebral  cortex.  The  neurones  of  the  lateral  nucleus  are,  the 
greater  number,  of  medium  size,  though  some  are  small  and  a 
few  are  of  large  size.  They  fall  into  three  groups,  the  inter- 
nuncial, the  thalamo -cortical  and  the  thalamo -spinal.  Fine 
and  medium  internuncial  fibers  are  contributed  to  the  arcuate 
and  central  nuclei,  from  which  and  the  medial  nucleus  the 
lateral  nucleus  receives  internuncial  fibers.  The  thalamo- 
cortical  fibers  are  numerous;  they  enter  the  cortical  fillet  and 
terminate  in  the  posterior  part  of  the  frontal  gyri,  the  central 
gyri,  the  fronto-parietal  operculum,  the  paracentral  gyrus  and, 
probably,  in  the  gyrus  cinguli.  By  far  the  greater  number  end 
anterior  to  the  central  sulcus  (Ernest  Sachs);  many  of  these 


224 


THE    CEREBRUM 


Fig.  89. — Transverse  section  of  the  brain  in  the  line  of  the  pyramidal  tracts, 
showing  basal  ganglia,  internal  capsules,  corpus  callosum,  lateral  and  third 
ventricles,  etc.     Viewed  from  front.     (Morris's  Anatomy  after  Toldt.) 

a.  Longitudinal  fissure,  b.  Radiation  of  corpus  callosum.  c.  Septum  pellucidum.  d, 
Chorioid  plexus  of  lateral  ventricle,  e.  Corona  radiata.  f .  Column  of  fornix,  g.  Chorioid 
plexus  of  third  ventricle,  h.  Internal  capsule,  i.  Thalamus,  j.  Third  ventricle,  k. 
Interpeduncular  fossa.  1.  Inferior  horn  of  lateral  ventricle,  m.  Cerebral  peduncle,  n. 
Brachium  pontis.  o.  Longitudinal  pyramidal  fasciculi  of  pons.  p.  Cerebellum,  q.  Deep 
fibers  of  pons.  r.  Pyramid,  s.  Superior  frontal  gyrus,  t.  Body  of  corpus  callosum. 
u.  Anterior  horn  of  lateral  ventricle,  v.  Head  of  caudate  nucleus,  w.  Radiation  of 
corpus  striatum,  x.  Putamen.  y.  External  capsule,  z.  Insula,  aa.  Claustrum.  bb. 
Globus  pallidus.  cc.  Optic  tract,  dd.  Corpus  mammillare.  ee.  Oculo-motor  nerve. 
ft.  Trigeminal  nerve,  gg.  Facial  and  acoustic  nerves,  hh.  Flocculus,  ii.  Glossopharyn- 
geal nerve,     jj.  Vagus  nerve,     kk.  Inferior  olivary  nucleus.     11.  Decussation  of  pyramids. 


COMMON   SENSORY   PATHS  2  2$ 

anterior  fibers  are  of  medium  size,  though  there  are  a  few  coarse 
and  fine  fibers  interspersed.  Many  fine  and  a  few  medium 
fibers  terminate  behind  the  central  sulcus.  The  thalamo- 
spinal  fibers  are  traced  by  Sachs  from  the  extreme  ventral  part 
of  the  lateral  nucleus  (ventral  nucleus)  downward  along  the 
medial  longitudinal  bundle.  He  describes  collaterals  to  cra- 
nial nuclei  (as  the  V,  VI,  X).  Sachs  found  no  other  descending 
fibers;  but  J.  S.  Collier  has  traced  a  tract,  in  the  cat,  from  the 
thalamus  down  the  lateral  column  of  the  spinal  cord.  It 
descends  with  the  rubro-spinal  tract. 

Five  paths  for  common  sensory  imptilses  from  thalamus  to 
cerebral  cortex  (Head  and  Holmes).  These  paths  carry:  (i) 
Impulses  of  posture  and  passive  movement  (muscle  sense)  and 
tension  impulses,  enabling  one  to  estimate  lifted  weights.  (2) 
Impulses  of  light  touch  and  pressure  touch  (tactile  sensibility) 
making  it  possible  to  estimate  weights  on  supported  hands. 
(3)  Impulses  of  tactile  or  spacial  discrimination  produced  by 
two  or  more  simultaneous  contacts.  These  underlie  recogni- 
tion of  size,  shape  and  form  in  three  dimensions.  (4)  Impulses 
localizing  successive  points  of  contact,  tactile  localization. 
(5)  Thermal  impulses  discriminating  between  degrees  of  heat 
and  cold. 

The  impulses  traversing  these  five  paths  must  evoke  their 
appropriate  sensations  in  the  cortex.  Painful  and  pleasurable 
sensations  arise  in  the  thalamus.  Temperature  impulses  excite 
sensations  in  the  thalamus,  also;  but  they  are  often  painful  or 
pleasant  rather  than  thermal  fBrain,  Vol.  34). 

Destructive  lesions  of  the  lateral  nucleus,  according  to  size 
and  location,  cause  exaggerated  response  to  painful  and  pleasur- 
able stimuli,  or  a  degree  of  anaesthesia  and  ataxia  on  the  opposite 
side  of  the  body. 

7.  The  nucleus  of  the  pulvinar  (Fig.  56)  is  an  important  one. 
It  receives  about  20  per  cent,  of  the  optic  fibers  and  gives  rise  to 
a  corresponding  number  of  the  corticipetal  fibers  in  the  optic,  or 
thalamo-occipital  radiation;  hence,  a  lesion  of  the  pulvinar 
impairs  vision.     It  is  continuous  with  the  lateral  nucleus. 

The  white  matter  of  the  thalamus  includes,  first,  the  stratum 

IS 


226  THE    CEREBRUM 

zonale  of  the  superior  and  medial  surface,  which  is  derived  from 
the  occipito-thalamic  radiation  and  the  lateral  root  of  the  optic 
tract,  and  the  zona  lateralis  of  the  lateral  surface;  and,  second, 
the  interior  fibers,  a  part  of  which  form  the  internal  medullary 
lamina.  Into  the  thalamus  enter  the  medial  fillet,  the  spino- 
thalamic tract,  a  small  part  of  the  medial  longitudinal  bundle, 
the  brachium  conjunctivum  cerebelli  and  perhaps  some  other 
tegmental  fibers,  all  carrying  common  sensory  impulses;  they 
end  chiefly  in  the  lateral  nucleus,  whence  the  cortical  fillet 
proceeds  to  the  cerebral  cortex.  The  thalamus  also  receives 
fibers  from  the  special  sense  paths,  from  the  optic,  auditory, 
olfactory,  and  the  gustatory,  and  gives  rise  to  fibers  that  con- 
tinue in  those  paths  to  the  special  sense  areas  of  the  cortex. 
It  is  also  known  that  the  thalamus  is  entered  by  a  considerable 
number  of  corticifugal  fibers,  especially  through  the  occipito- 
thalamic  and  temporo-thalamic  radiations.  Besides  the  inter- 
nuncial  fibers  that  associate  the  different  thalamic  nuclei 
together,  the  thalamus  has  either  a  genetic  or  terminal  relation 
to  the  following  fasciculi: 

1.  The  columna  of  the  fornix,  having  pierced  the  thalamus, 
descends  to  the  corpus  mammillare  and  terminates  in  its  medial 
nucleus,  whence  the  bundle  of  Vicq  d'Azyr,  the  mammillo- 
thalamic  bundle,  rises  and  ascends  to  the  thalamus.  It  ends  in 
the  anterior  nucleus. 

2.  The  stria  medullaris  thalami  (Fig.  87)  from  the  hippocam- 
pus and  from  the  region  of  the  olfactory  triangle,  terminates 
partly  in  the  tectum,  but  chiefly  in  the  nucleus  habenulae  and 
from  this  nucleus  the  fasciculus  retroflexus  or  habenulo-peduncu- 
laris  originates  and  descends  to  the  interpeduncular  nucleus. 
Both  "one*'  and  "two"  belong  to  the  olfactory  paths. 

3.  The  ventral  stalk  of  the  thalamus,  connected  with  its  ven- 
tro  lateral  part,  is  a  compound  funiculus  situated  below  the 
lentiform  nucleus;  it  contains  afferent  and  efferent  fibers  and  is 
often  called  ansa  peduncularis.  It  is  divided  by  the  nucleus 
interansalis  into  {a)  an  upper  stratum  and  (6)  a  lower  stratum. 
{a)  The  upper  stratum,  the  ansa  lenticularis,  is  made  up  of 
thalamo-striate    and    of    hypothalamo-striate    fibers,    joining 


227 


LATERAL 
GENICU- 
LATE   BODY 


Fig.  90. — The  optic  path.     {Original.) 


228  THE    CEREBRUM 

lateral  nucleus  and  hypothalamic  nucleus  with  globus  pallidus; 
and  these  fasciculi  are  intermingled  with  strio-fugal  fibers.  The 
strio-fugal  fibers  connect  the  globus  pallidus  with  the  thalamus, 
red  nucleus,  h3^othalamic  nucleus  and  substantia  nigra,  (b) 
The  lower  stratum,  the  inferior  peduncle  of  the  thalamus,  contains 
cortico-thalamic  fibers  which  connect  the  temporal  and  insular 
cortex  with  the  lateral  nucleus  of  the  thalamus  (Villiger). 

The  common  afferent  thalamo-cortical  fibers  already  de- 
scribed on  pp.  102-103  form  the  parietal  and  frontal  stalks  of 
the  thalamus.  They  are  axones  of  the  lateral  nucleus  which 
terminate  in  the  central,  the  posterior  part  of  the  frontal  and 
the  middle  of  the  cingulate  gyri;  they  are  intermingled  with  cor- 
tico-thalamic fibers.     They  constitute  the  cortical  fillet. 

4.  The  parietal  stalk,  comprising  five  specific  bundles,  ascends 
through  the  occipital  part  of  the  internal  capsule;  it  contains  the 
common  sensory  fibers  going  to  the  posterior  central  gyrus  and 
the  adjacent  part  of  the  paracentral  gyrus  (the  true  somaesthetic 
area)  as  well  as  many  fibers  to  the  motor  and  psychic  motor  area. 

5.  The  frontal  stalk  of  the  thalamus  rises  in  the  anterior  part 
of  the  lateral  nucleus;  it  traverses  the  frontal  part  of  the  capsule 
and  terminates  in  frontal  cortex.  Like  that  part  of  the  parietal 
stalk  which  ends  anterior  to  the  central  sulcus,  the  frontal  stalk 
is  probably  concerned  with  the  automatic  control  of  the  dis- 
charge of  motor  impulses  from  the  emissive  motor  center. 

Metathalamus.— This  embraces  the  medial  and  lateral  gen- 
iculate bodies  which  were  described  on  p.  140,  164.  Both 
contain  thalamo-cortical  and  thalamo-tectal  (thalamo-quadri- 
geminate)  neurones.  The  latter  send  their  axones  to  the 
quadrigeminal  coUiculi  through  the  brachium  inferius  and 
brachium  superius;  while  the  axones  of  the  former  enter  into 
their  respective  radiations. 

I.  Optic  Radiation  (Gratioleti). — The  optic  radiation  is  a 
two-way  funiculus  composed  of  afferent  special  sense  fibers  and 
efferent,  reflex  fibers.  The  afferent  fibers,  thalamo-occipital 
fasciculus,  rise  in  the  lateral  geniculate  body  and  the  pulvinar 
of  the  thalamus  and  carry  the  visual  impulses  through  the  inter- 
nal capsule  to  the  striated  cortex  along  the  calcarine  fissure, 


ACUSTIC  RADIATION  229 

where  they  evoke  the  sensation  of  sight.  The  efferent,  occipito- 
thalamic  fibers  rise  from  the  large  solitary  pyramids  of  Meynert 
in  the  visual  cortex;  they  descend  through  the  optic  radia- 
tion to  the  lateral  geniculate  body  and  thalamus  and,  through 
the  brachium  superius,  some  continue  to  the  superior  quad- 
rigeminal  colliculus.  In  the  superior  colliculus  contacts  are 
formed  with  tecto-spinal  neurones  whose  axones  end  in  motor 
nerve  nuclei,  cranial  and  spinal.  Destruction  of  the  optic 
radiation  on  one  side  causes  blindness  in  the  opposite  half  of  the 
visual  fields,  homonymous  hemianopsia^  without  loss  of  optic 
reflexes. 

2.  The  acustic  radiation,  like  the  optic,  is  a  double  funiculus 
of  afferent  and  efferent  fibers.  The  afferent,  ihalamo-temporal 
fibers  rise  in  the  medial  geniculate  body;  they  run  through  the 
internal  capsule  just  behind  the  optic  radiation,  and  terminate 
in  the  transverse  and  superior  temporal  gyri;  there,  the  impulses 
from  the  cochlear  nerve  excite  the  sensations  of  sound.  In  the 
acustic  cortex  rise  the  efferent,  temporo-thalamic  fibers  which  have 
a  reflex  function.  Traversing  the  acustic  radiation  in  a  descend- 
ing direction,  they  reach  the  medial  geniculate  body  and  the 
greater  number  continue  through  the  brachium  inferius  to  the 
inferior  quadrigeminal  colliculus,  the  acustic  reflex  center.  If 
the  acustic  radiation  is  destroyed  on  one  side  the  result  is  deaf- 
ness in  the  opposite  ear. 

The  red  nucleus  {nucleus  ruber)  of  the  tegmentum  is  situated 
beneath  the  thalamus  (Figs.  54  and  58).  See  p.  139.  It  is 
a  relay-station  in  the  indirect  afferent  path,  receiving  the  oppo- 
site brachium  conjunctivum  cerebelli  and,  by  its  axones,  the 
rubro-thalamic  tract,  continuing  the  path  to  the  thalamus.  It 
also  receives  efferent  axones  from  the  cerebral  cortex  (Beevor 
and  Horsley)  and  globus  pallidus  and  gives  origin  to  one  cen- 
trifugal bundle  of  axones,  the  rubrospinal  tract,  which  after 
crossing  over  in  the  ventral  decussation  of  the  tegmentum 
(Forel's)  descends,  first,  with  the  medial  portion  of  the  lateral 
fillet;  second,  through  the  lateral  area  of  the  medulla,  and, 
third,  through  the  lateral  part  of  the  spinal  cord.  Gradually 
diminishing,  it  disappears  at  the  first  lumbar  segment.     It 


230 


THE   CEREBRUM 


B 


■  ■'•It  ^^ 


y  { 


■44.     •.,  ■  s'  .■  * 


•  H- ■•.■.';« 


V 


•   v» 


1  M. 


••\ 


vk\ 


.  \\^'  '••  ••    Au.  "A 


\. 


^ 


■\-^.«V\-\V-_/    \\-\     } 


Fig.  91. — Cell  and  fiber  lamination  in  the  uncus  hippocampi  (lobus  pyri- 
formis).  The  area  of  smell.  (After  A.  W.  CamphelVs  "Histological  Studies 
on  the  Localization  of  Cerebral  Function."  Published  by  the  Syndics  of  the 
Cambridge  University  Press.) 

A.  Showing  fibers.  B.  Showing  cell-bodies,  z.  Stratum  zonale,  external  medullary 
lamina,  s.  Supraradiary  zone  containing  radiating  fibers.  B.  Line  of  Baillarger.  R. 
Radiaryzone.  i.  Plexiform  layer.  2.  Layer  of  stellate  cells  showing  cell-nests.  3.  Repre- 
sents third  and  fourth  layers  of  typical  cortex,  medium-sized  pyramids  obliquely  placed  and 
stellate  cells;  with  Golgi's  silver  method  shows  tassel-cells.  4.  Fusiform  or  triangular  cells. 
S.  Medium-pyramids.     6.  Fusiform  cells. 


HIPPOCAMPAL   FORMATION 


231 


ends  in  the  gray  crescent  of  the  spinal  cord.  The  red  nucleus 
contains  ruhro-thalamic  and  rubrospinal  neurones.  The  rubro- 
thalamic fasciculus  terminates  in  the  lateral  nucleus  of  the  thala- 
mus; it  continues  the  cerebellar  path  from  the  brachium  con- 
junctivum,  though  a  part  of  the  brachium  continues  without 


Fig.  92. — Transverse  section  of  the  hippocampal  formation.     (After  Edinger.) 
A.  Nucleus  of  fascia  dendata. 

interruption  to  the  thalamus.  The  rubrospinal  fasciculus  ends 
in  motor  nuclei,  cranial  and  spinal.  The  latter  bundle,  accord- 
ing to  Horsley,  is  a  part  of  the  coordinating  mechanism  for 
locomotion.  The  rubro-thalamic  fasciculus  belongs  to  the  indi- 
rect afferent  path. 


232  THE    CEREBRUM 

The  nucleus  hypothalamicus  (Luysi)  (Figs.  37  and  54)  is  a 
pigmented  bi-convex  mass  of  gray  matter  placed  ventro-lateral 
to  the  red  nucleus,  and  between  it  and  the  basis  pedunculi.  See 
p.  139.  It  is  separated  from  the  red  nucleus  by  the  zona 
incerta.  It  constitutes  an  important  terminal  nucleus  for  cer- 
tain corticipetal  fibers  of  the  tegmentum  and  gives  origin  to 
others.  Certain  descending  fibers  from  the  striate  body  ter- 
minate in  this  nucleus.  The  latter  in  part  run  through  the 
tuber  cinereum,  just  above  the  posterior  border  of  the  optic 
chiasma,  and  form  the  commissura  superior  (Meynerti),  Gudden's 
commissure  being  called  the  commissura  inferior.  The  hypo- 
thalamic nucleus  is  closely  associated  with  the  globus  pallidus  of 
the  lentiform  nucleus;  it  is  not  connected  with  the  thalamus. 
Besides  receiving  the  afferent  tegmental  fibers,  it  receives  the 
strio-hypothalamic  fasciculus  and  its  axones  form  the  hypo- 
thalamo-striate  fasciculus,  bundles  which  doubly  connect  the 
nucleus  with  the  globus  pallidus. 

The  superior  colliculi  of  the  corpora  quadrigemina  (Figs.  58 
and  63)  represent  the  optic  lobes  of  birds,  fishes  and  reptiles. 
They  contain  the  center  of  optic  reflexes.  In  being  stratified, 
they  bear  some  resemblance  to  the  lateral  geniculate  bodies. 
They  possess  three  white  and  two  gray  layers:  (i)  The  stratum 
zonale  (stratum  album  superficial)  is  a  layer  of  white  matter  on 
the  surface.  This  invests  (2)  the  laminated  stratum  griseum, 
which  forms  the  deep  part  of  the  colli  cuius  and  lies  upon  (3)  the 
stratum  album  profundum.  The  stratum  griseum  superficial  is 
composed  of  small  mutlipolar  cells.  The  stratum  album  medium 
is  a  layer  of  fibers  separating  the  small  from  the  large  multipolar 
cells.  The  large  cells  make  up  the  stratum  griseum  profundum, 
underneath  which  is  the  deep  layer  of  fibers,  the  stratum  album 
profundum.  The  fibers  of  the  superficial,  middle  and  deep 
strata  comprise,  first,  those  that  enter  the  colHculus  through  the 
brachium  superius,  through  the  superior  and  a  part  of  the 
lateral  fillet  and  the  spino-thalamic  tract;  and,  second,  those 
that  take  origin  in  the  coUiculus  and  leave  it  through  the  brach- 
ium superius  or  the  tecto-spinal  fasciculi  and  other  descending 
bundles.     Of  the  fibers  originating  in  the  superior  colli  cuius  and 


TECTAL  FASCICULI  233 

running  through  the  brachium  superius  it  is  supposed  that  some 
go  as  far  as  the  retina;  probably  others  enter  the  cortical  fillet. 
The  descending  axones  of  the  superior  colliculus  joined  by  a 
smaller  number  from  the  inferior  colliculus,  constitute  the  tecto- 
spinal and  the  tecto-cerebellar  fasciculi  and  a  part  of  the  tecto- 
pontal  and  tecto-reticular  fasciculi  which  rise  chiefly  in  the  infe- 
rior colliculus. 

The  tecto-cerebellar  fasciculi  enter  the  cerebellum  through  the 
superior  medullary  velum;  they  bring  the  cerebellum  into  the 
olfactory,  visual  and  acustic  (cochlear)  correlations. 

The  tectospinal  fasciculi  are  two  in  number,  an  anterior  and  a 
lateral.  The  short  fibers  of  these  tracts  end  in  the  cranial  nerve 
nuclei  and  form  the  tecto-hulhar  fasciculi.  Formerly  the  anterior 
tecto-spinal  fasciculus  was  called  the  anterior  longitudinal 
bundle.  The  anterior  tecto-spinal  fasciculus  is  made  up  chiefly 
of  efferent  axones  of  the  cell-bodies  in  the  superior  colliculus.  It 
crosses  at  once  through  the  dorsal  tegmental  decussation  (Fig. 
6^))  and  descends  ventro-lateral  to  the  opposite  medial  longi- 
tudinal bundle,  to  the  anterior  columna  of  gray  matter  in  the 
spinal  cord.  Its  fibers  end  largely  in  the  nuclei  of  the  third, 
fourth  and  sixth  cerebral  nerves  and  in  the  cervical  enlargement 
of  the  spinal  cord;  but  perhaps  others  enter  the  remaining  nuclei 
of  motor  cerebral  nerves,  and  a  few  fibers  of  the  tract  have  been 
traced  as  low  as  the  lumbar  region.  This  bundle  is  the  great 
optic  reflex  tract.  The  fibers  to  the  nuclei  of  the  third,  fourth 
and  sixth  cerebral  nerves  bring  about  the  reflex  movements  of 
the  eyeball,  contraction  of  the  pupil  and  accommodation  to 
distance;  while  those  fibers  which  end  in  the  gray  substance  of 
the  lower  part  of  the  cervical  enlargement  of  the  spinal  cord, 
called  the  cilio-spinal  center,  through  the  white  rami  communi- 
cantes  and  cervical  sympathetic,  produce  dilatation  of  the  pupil. 
The  latter  constitute  the  pupillo-dilator  tract. 

The  lateral  tecto-spinal  fasciculus  has  the  same  origin  as  the 
aw^mor  fasciculus;  but  it  is  largely  if  not  wholly  uncrossed.  It 
descends  through  the  lateral  part  of  the  reticular  formation  and 
the  lateral  column  of  the  spinal  cord  in  close  relation  with  the 
thalamo-spinal  and  rubro-spinal  bundles.     The  fibers  of  the 


234  THE   CEREBRUM 

lateral  tecto-spinal  fasciculus  end  in  the  gray  matter  of  the  brain 
stem  and  spinal  cord. 

Destructive  lesions  affecting  the  superior  quadrigeminal  col- 
liculi  produce  loss  of  reflex  movement  of  the  eyeballs,  loss  of 
pupillary  reflex  and  loss  of  accommodation. 

The  inferior  colliculi  of  the  corpora  quadrigemina  form  a 
relay  in  the  auditory  path  (Figs.  62  and  64).  They  are  made 
up  of  a  white  stratum  zonale,  whose  fibers  are  continuous 
chiefly  with  the  lateral  fillet  and  brachium  inferius,  and  of  a 
deep  gray  mass,  the  nucleus  colliculi  inferioris,  which  is  com- 
posed of  small  multipolar  cell-bodies  in  a  network  of  fibers. 
The  nucleus  rests  upon  the  stratum  album  profundum.  The 
nuclei  of  the  two  eminences  fuse  in  the  median  plane.  In  the 
nuclei  end  a  considerable  number  of  fibers  belonging  to  both 
lateral  fillets,  but  most  of  them  belong  to  that  of  the  same  side; 
and  from  them  proceed  axones  of  the  auditory  paths  through 
the  brachia  inferiora  to  the  medial  geniculate  bodies.  At  this 
level  the  acustic  path  becomes  entirely  crossed.  A  few  fibers 
of  the  spino-thalamic  tract  also  end  in  the  inferior  colliculus. 
Again  this  colliculus  receives  corticifugal  fibers  of  the  temporo- 
thalamic  radiation. 

Axones  from  the  nucleus  of  the  inferior  colliculus  either  run 
forward  through  the  brachium  inferius  to  the  medial  geniculate 
body,  with  the  lateral  fillet  forming  a  segment  of  the  acustic 
path,  or  they  descend  in  the  tecto-spinal,  tecto-cerebellar,  tecto- 
pontal  and  tecto-reticular  fasciculi.  The  first  two,  which  rise 
chiefly  in  the  superior  colliculus,  have  been  described. 

The  tecto-pontal  fasciculus  (of  Miinzer)  rises  largely  in  the 
inferior  colliciilus  and  ends  within  the  nucleus  pontis. 

The  tecto-reticular  fasciculus  (of  Pawlow)  is  a  small  bundle 
rising  in  the  quadrigeminal  region  and,  as  its  name  indicates, 
terminating  in  the  nuclei  of  the  reticular  formation,  chiefly 
in  the  pons. 

Though  the  greater  part  of  the  lateral  fillet  passes  by  the 
inferior  colliculus  without  relay,  a  lesion  in  this  body  is  apt  to 
involve  the  entire  bundle  and  cause  almost  complete  deafness 
in  the  opposite  ear. 


CENTRAL  GRAY  MATTER  235 

Nucelus  Lateralis  Superior  (Fig.  63). — In  the  reticular  for- 
mation of  the  tegmentum  at  the  level  of  the  superior  quad- 
rigeminal  colliculus  is  the  nucleus  lateralis  superior.  It  con- 
tains large  multipolar  cell-bodies  and,  being  imbedded  deeply 
in  the  tegmentum  it  is  properly  called  nucleus  tegmenti 
profundus  (see  pp.  151  and  155).  The  nucleus  forms  a  relay 
both  for  ascending  and  descending  paths  of  the  formatio  reticu- 
laris. According  to  Tschermak,  a  small  fasciculus  runs  from 
this  nucleus  into  the  medial  longitudinal  bundle  where  it 
divides  T-like;  and  its  descending  fibers  run  down  through  the 
anterior  fasciculus  proprius  of  the  cord  (Barker).  This  is  the 
anterior  reticulospinal  fasciculus,  an  uncrossed  tract.  Other 
axones  of  the  nucleus  tegmenti  profundus  decussate  in  the  mid- 
brain and  descend  as  lateral  reticulospinal  fasciculus  described 
on  p.  155. 

Substantia  Nigra  (Figs.  61,  62,  62,  and  64). — The  small  pig- 
mented multipolar  cell-bodies  which  make  up  the  substantia 
nigra  form,  first,  a  terminal  nucleus  for  certain  fibers  of  the 
medial  fillet  and  a  nucleus  of  origin  for  other  fibers  which  con- 
tinue in  that  tract  (Barker);  and,  second,  a  terminal  station 
for  the  fasciculus  habenulo-peduncularis,  or  retroflexus  (Mey- 
nerti)  and  a  relay  between  the  globus  pallidus  and  nucleus 
pontis. 

m.  CENTRAL  OR  VENTRICULAR  GRAY  MATTER 

It  is  located  (i)  in  the  floor  and  walls  of  the  third  ventricle, 
the  hypothalamus;  (2)  in  the  middle  commissure  of  that  ven- 
tricle, the  massa  intermedia;  and  (3)  around  the  cerebral 
aqueduct,  the  stratum  griseum  centrale. 

I.  The  Hypothalamus,  Pars  Optica. — The  lamina  cinerea 
terminalis  and  the  tuher  cinereum  (Figs.  21  and  33)  form  a  sheet 
of  gray  substance  that  connects  the  inferior  and  medial  sur- 
faces of  the  cerebral  hemispheres.  The  tuber  cinereum,  on 
each  side  of  the  median  line,  contains  a  small  triple  nucleus, 
the  supraoptic  nucleus  of  Cajal.  It  is  made  up  of  an  anterior, 
a  posterior  and  a  dorsal  cell-group.  It  is  not  surely  known 
whether  any  fibers  of  the  superior  commissure  or  inferior  com- 


236  THE   CEREBRUM 

missure  rise  or  terminate  in  this  nucleus;  nor  is  the  relation 
to  it  of  the  basal  bundle  of  Wallenberg,  the  oljacto-mesencephalic 
fasciculus,  understood.  Probably  a  part  of  this  path  is  relayed 
in  the  supraoptic  nucleus.  The  optic  chiasma  is  white  matter, 
and  the  hypophysis  is  not  composed  of  nerve  tissue  at  all  and, 
therefore,  neither  one  need  be  described  in  this  place.  From 
the  floor  of  the  third  ventricle  the  gray  matter  extends  laterally 
beneath  the  thalamus,  and  is  continuous  with  the  anterior 
perforated  substance.  The  gray  matter  of  the  floor  also  ex- 
tends up  to  the  sulcus  hypothalamicus  on  the  medial  surface 
of  the  thalamus.  The  tuber  cinereum  receives  efferent  fibers 
from  the  corpus  striatum  of  both  sides.  Some  of  these  fibers 
form  a  commissure  just  above  that  of  Gudden ;  hence  it  is  called 
the  commissura  superior  (Meynerti)  to  distinguish  it  from  the 
commissura  inferior  (Guddeni)  in  the  optic  chiasma.  The 
fibers  of  Meynert's  commissure  cross  through  the  tuber  ciner- 
eum anterior  to  infundibulum. 

Hypothalamus,  Pars  Mammillaris  (Figs.  31  and  58). — The 
corpora  mammillaria  (albican tia),  though  composed  of  fornix 
fibers  on  the  surface,  contain  in  the  interior  two  nuclei,  the 
medial  and  lateral.  The  mediaVnucleus  is  the  larger  of  the  two. 
It  receives  the  end-tufts  of  the  fibers  in  the  columna  of  the  fornix 
and  gives  origin  to  internuncial  fibers,  connecting  it  with  the 
lateral  nucleus,  and  to  the  fasciculus  mammillaris  princeps. 
The  latter  bifurcates,  sending  one  branch,  the  mammillo- 
thalamic  bundle  (of  Vicq  d'Azyr),  up  to  the  anterior  nucleus 
of  the  thalamus  and  the  other  branch,  the  fasciculus  mammillo- 
tegmentalis,  backward  into  the  tegmentum.  The  fasciculus 
mammillo-thalamicus  (Vicq  d'Azyri)  connects  the  fornix  with 
the  thalamus.  The  mammillo-tegmental  bundle  descends  to 
the  nucleus  tegmenti  profundus  and  central  gray  matter  of  the 
mid-brain;  some  of  its  fibers  continue  along  the  medial  longi- 
tudinal bundle  into  the  reticular  formation  of  the^pons  and 
medulla,  probably  ending  in  various  efferent  nuclei. 

The  small  lateral  nucleus  of  the  corpus  mammillare  gives 
origin  to  the  peduncle  of  the  mammillary  body,  which  accord- 
ing to  Flechsig  ends  in  the  nucleus  tegmenti  dorsalis  and  the 


CENTRAL  GRAY  MATTER  237 

substantia  grisea  centralis  of  the  mid-brain  and  is  thence  con- 
nected with  the  motor  nerve-nuclei  and  the  automatic  centers 
of  the  medulla  by  the  dorsal  longitudinal  bundle  of  Schiitz. 
Through  the  fornix,  the  stria  medullaris  thalami,  thehabenulo- 
peduncular  tract  and  the  descending  axones  of  the  inter- 
peduncular nucleus;  through  the  fornix,  the  mammillo-thalamic 
bundle  and  the  thalamo-spinal  fasciculus;  through  the  mam- 
millo-tegmental  tract,  the  peduncle  of  the  mammillary  body, 
the  olfacto-mesencephalic  bundle  and  the  dorsal  longitudinal 
bundle  of  Schiitz,  etc.,  some  of  the  reflex  connections  of  the 
olfactory  nerves  are  established. 

2.  The  massa  intermedia  {the  middle  commissure,  Figs.  33 
and  87)  joins  the  medial  nuclei  of  the  thalami.  It  is  formed, 
when  present,  by  the  approximation  and  fusion  of  the  thalami 
in  the  second  month  of  embryonic  life.  It  is  occasionally  ab- 
sent. In  the  massa  intermedia  are  cell-bodies  and  transverse 
fibers.  The  latter  appear  to  be  loops  which  reach  only  to  the 
median  line;  at  least  many  of  the  fibers  do  not  cross  to  the  oppo- 
site side.  It  receives  internuncial  fibers  from  the  thalamus 
(Sachs).  According  to  Cajal  the  massa  intermedia  of  the 
rabbit  contains  eight  distinct  nuclei.  It  appears  to  be  accessory 
to  the  medial  nucleus.  It  is  not  a  commissure  in  the  ordinary 
sense  of  that  term. 

3.  The  stratum  griseum  centrale  of  the  mid-brain  (Figs. 
58,  62  and  64)  surrounds  the  cerebral  aqueduct  (Sylvii).  This 
gray  matter  begins  in  the  lateral  wall  of  the  third  ventricle.  It 
extends  through  the  mid-brain  and  is  continuous  with  the  gray 
substance  in  the  floor  of  the  fourth  ventricle.  Besides  the  nuclei 
of  the  third,  fourth  and  a  part  of  the  fifth  cerebral  nerves  and 
the  nucleus  tegmenti  dorsalis,  it  contains  scattered  cell-bodies  of 
variable  size  and  shape  which  give  origin  to  the  true  commissural 
fibers  of  the  posterior  commissure.  The  central  gray  substance 
of  the  mid-brain,  together  with  its  nucleus  tegmenti  dorsalis, 
receives  the  peduncle  of  the  mammillary  body  and  a  part  of  the 
mammillo-tegmental  fasciculus,  and  it  originates  the  dorsal 
longitudinal  bundle  of  Schiitz,  which  descends  to  the  genetic 
nuclei  of  the  pons  and  medulla. 


238  THE    CEREBRUM 

Oculomotor  Nucleus  (Figs.  59  and  61). — The  nucleus  of  the 
third  cerebral  nerve  (nucleus  nervi  oculomotorii)  is  an  elongated 
mass  of  gray  substance  in  the  ventral  part  of  the  stratum  gri- 
seum  centrale,  which  extends  from  the  lateral  wall  of  the  third 
ventricle  down  to  the  level  of  the  transverse  groove  between  the 
quadrigeminal  coUiculi.  The  nuclei  are  placed  somewhat 
obliquely;  at  the  lower  end  they  fuse  in  the  median  plane.  As 
was  stated  in  the  section  on  the  mid-brain  (p.  150)  the  oculomotor 
nucleus  is  composed  of  a  visceral  and  a  somatic  part;  the  former 
innervates  smooth  muscles  within  the  eye  and  the  latter  sup- 
plies striated  muscles  outside  the  eyeball. 

The  greater  number  of  axones  of  this  nucleus  ran  forward  into 
the  nerve  of  the  same  side;  but  those  from  the  median  nest  go 
into  both  nerves,  and  a  small  bundle  from  each  nucleus  descends 
with  the  medial  longitudinal  bundle  to  the  colliculus  facialis, 
where  it  joins  the  facial  nerve  and  through  that  nerve  supplies 
the  muscles  of  facial  expression  above  the  orbit.  There  is  un- 
certainty concerning  the  origin  of  this  latter  bundle;  it  may  rise 
in  the  superior  part  of  the  facial  nucleus. 

Trochlear  Nucleus  (Fig.  62). — The  nucleus  nervi  trochlearis 
is  a  small  oval  mass  of  cell-bodies  situated  at  the  level  of  and 
anterior  to  the  inferior  colliculus  of  the  corpora  quadrigemina. 
It  is  in  the  ventral  part  of  the  stratum  griseum  centrale  like  the 
oculomotor  nucleus.  It  is  a  purely  somatic  nucleus,  supplying 
one  striated  muscle.  Unlike  the  third,  the  axones  from  the 
nucleus  of  the  fourth  cerebral  nerve  run  backward  and  issue  from 
the  posterior  surface  of  the  brain-stem  at  the  isthmus ;  they  are 
peculiar  also  in  that  the  axones  decussate  before  their  emergence 

(Fig.  56). 

The  nuclei  of  the  oculomotor  and  trochlear  nerves  receive 
fibers  from  the  cerebral  cortex  through  the  pyramidal  tract  and 
other  motor  tracts  of  the  internal  capsule  and  thus  obtain  their 
voluntary  motor  and  inhibitory  impulses.  It  is  probable  also 
that  the  third  nucleus  receives  fibers,  through  the  medial  longi- 
tudinal bundle,  from  the  opposite  abducent  nucleus,  and  that 
the  part  of  the  nucleus  which  receives  these  fibers  supplies  the 
medial  rectus  muscle  of  the  eye.     For  the  purpose  of  reflex 


TRIGEMINAL  NUCLEUS  239 

both  the  oculomotor  and  trochlear  nuclei  receive  fibers  from  the 
anterior  tecto-spinal  and  medial  longitudinal  bundles,  from 
the  mammillary  peduncle  and  the  mammillo-tegmental  fasc- 
iculus and,  perhaps,  from  the  cerebellum  through  the  brachia 
conjunctiva. 

Trigeminal  nucleus  of  the  mid-brain  is  a  very  small  nucleus 
situated  in  the  extreme  lateral  part  of  the  central  gray  matter. 
It  is  continuous  with  the  pontine  nucleus  of  the  fifth,  located 
under  the  locus  caeruleus,  and  is  merely  the  superior  end  of  the 
motor  nucleus  of  the  trigeminal.  It  gives  origin  to  the  mesen- 
cephalic root  of  the  fifth  nerve,  which  descends  to  the  pons  and 
there  joins  the  main  motor  root.  In  its  course  downward  the 
mesencephalic  root  runs  between  the  cental  gray  matter  and  the 
brachium  conjunctivum  cerebelli.  It  contains  a  few  ascend- 
ing fibers  from  the  sensory  root  (reflex). 

Otto  May  and  Sir  Victor  Horsley,  in  Brain,  Vol.  33,  support 
this  view  of  the  mesencephalic  nucleus  of  the  trigeminal  nerve, 
but  the  work  of  J.  B.  Johnston  should  be  examined.  By  an 
abundance  of  comparative  evidence  Johnston  revives  the  view 
formerly  held,  that  the  mesencephalic  root  joins  the  sensory 
root  of  the  trigeminal  nerve,  not  the  motor.  Johnston^s  views 
are  as  follows :  The  mesencephalic  nucleus  lies  in  the  dorsal  zone 
(the  afferent  zone)  of  the  neural  tube;  it  is  a  part  of  the  neural 
crest  included  in  the  dorsal  lamina  of  the  tube  and  is  analogous 
to  a  ganglion;  its  cells  are  similar  to  those  of  a  spinal  ganglion  in 
man  and  to  the  giant  cells  in  the  spinal  cord  of  fishes,  being 
pear-shaped  and  fusiform  bipolars;  the  fibers  contributed  to  the 
mesencephalic  root  are  the  coarse  dendritic  processes,  while  the 
slender  processes,  the  axones,  terminate  within  the  tectimi; 
the  mesencephalic  root  joins  the  main  sensory  root  of  the  tri- 
geminal nerve  and,  probably,  is  sensory  in  function  (Jour. 
Comp.  Neurol,  and  Psychol.,  Vol.  19). 

Lesions  of  these  cerebral  nerve  nuclei  are  apt  to  involve  the 
tracts  of  the  tectum  and  tegmentum.  If  so,  the  result  is  paraly- 
sis of  the  nerves  on  the  same  side  and  hemianaesthesia,  hemi- 
ataxia,  loss  of  taste  (?)  and  deafness  on  the  opposite  side. 

The  white  matter  of  the  cerebrum  is  composed,  in  the  adult 


240  THE   CEREBRUM 

condition,  of  meduUated  fibers;  the  medullation  begins  in 
the  fourth  month,  in  utero,  and  is  continued  for  a  considerable 
time  after  birth  (Flechsig).  Within  the  cortical  substance  the 
myelin  sheaths  continue  to  be  laid  down  until  late  in  life  (Kaes, 
McMurrich).     The  cerebral  fibers  form  three  definite  systems: 

1.  Projection,  or  peduncular  fibers. 

2.  Transverse,  or  commissural  fibers. 

3.  Association  fibers. 

I.  PROJECTION  FIBERS 

The  projection  fibers  are  connected  only  with  the  motor  and 
sensory  areas  of  the  cerebral  cortex  and  are,  therefore,  motor  and 
sensory  in  function  (Figs.  74  and  75).  Where  they  are  present 
they  are  continuous  with  Meynert's  radiations.  They  are  com- 
posed, jirst^  of  the  medullated  axones  of  the  pyramids  and  the 
polymorphous  neurones;  these  descend  from  the  cerebral  cortex, 
are  motor  in  function,  or  corticifugal,  and  constitute  the  upper 
motor  segment;  and,  second,  they  comprise  the  medullated 
axones  of  neurones  whose  cell-bodies  are  situated  in  gray  matter 
below  the  cerebral  cortex;  these  axones  ascend  to  the  cortex  and 
are  sensory  in  function,  or  corticipetal.  The  projection  fibers 
run  from  cerebral  cortex  through  the  corona  radiata,  the  inter- 
nal capsule  and  the  mid-brain,  and  vice  versa  (Figs.  37  and  54). 
They  connect  the  cortex,  directly  or  indirectly,  with  all  parts 
of  the  body,  throwing  or  projecting  a  picture  of  every  part  and 
organ  upon  the  cerebral  cortex.  Many  of  the  paths  are  inter- 
rupted in  the  basal  ganglia,  especially  of  the  corticipetal  fibers. 
Within  the  hemisphere  all  projection  fibers  run  through  one 
great  sheet,  the  internal  capsule,  with  the  exception  of  the  olfac- 
tory; but  in  the  mid-brain,  they  are  separated  into  two  great 
groups — the  basis  pedunculi  and  the  tegmentum,  the  substantia 
nigra  intervening. 

CORTICIFUGAL,  OR  MOTOR  PROJECTION  FIBERS 

The  most  important  tracts  of  corticifugal  or  motor  projection 
fibers  are  the  following,  namely,  the  strio-fugal  fibers,  the  fronto- 
pontal  tract,  the  pyramidal  tract  and  the  temporo-pontal  tract. 


DESCENDING  FASCICULI  241 

The  strio-fugal  fasciculi  are  formed  by  axones  of  cell-bodies 
in  the  globus  pallidas  which  terminate  in  the  nucleus  hypo- 
thalamicus,  the  lateral  nucleus  of  the  thalamus,  the  nucleus 
ruber  and  the  substantia  nigra.  The  strio -hypothalamic  bundle 
appears  to  be  merely  associative  in  function;  the  other  three 
belong  to  long  conduction  paths.  The  strio-thalamic fasciculus 
ends  in  the  lateral  nucleus  of  the  thalamus;  but  is  connected 
with  lower  centers  by  the  thalamo-spinal  fasciculus  and,  per- 
haps, by  the  thalamo-olivary  fasciculus.  The  strio-ruhral  fasc- 
iculus is  an  important  bundle;  through  this  and  the  rubro- 
spinal fasciculus,  the  striate  body  exerts  its  steadying  effect  upon 
the  lower  motor  neurones.  The  strio-nigral  fasciculus  ends  in 
the  substantia  nigr;a,  whence  the  nigro-pontal  fasciculus  origi- 
nates and  continues  to  the  nucleus  pontis.  The  two  last  fasc- 
iculi form  the  intermediate  path  (Figs.  64  and  93). 

The  intermediate  path  {stratum  intermedium  pedunculi,  Figs. 
64,  93,  and  113)  extends  from  the  corpus  striatimi  through  the 
inferior  lamina  of  the  capsule  and  the  deep  part  of  the  basis 
pedunculi  to  the  motor  cerebral  nuclei  and  to  the  nucleus  pontis, 
though  it  is  relayed  in  the  substantia  nigra.  From  the  nucleus 
pontis  axones  run  by  way  of  the  brachium  pontis  to  the  cortex 
of  the  opposite  hemisphere  of  the  cerebellum.  The  intermedi- 
ate path  thus  forms  a  segment  of  an  indirect  (through  the  cere- 
bellum) efferent  and  probably  coordinating  path. 

The  fronto-pontal  tract  (tractus  cerebro-cortico-pontalis  fron- 
talis, Figs.  62,  93,  94  and  113)  rises  from  the  cortex  of  the  frontal 
lobe  anterior  to  the  precentral  sulci.  It  traverses  the  centrum 
semiovale,  corona  radiata,  frontal  part  of  the  internal  capsule 
and  medial  one-fifth  of  the  basis  pedunculi  to  the  ventral  area 
of  the  pons,  where  it  terminates  in  the  nucleus  pontis  (chiefly) 
and  in  the  nuclei  of  motor  cerebral  nerves  (Flechsig).  It  is 
probably  relayed  in  the  thalamus  (Beevor  and  Horsley). 

According  to  Dejerine,  the  temporo-pontal  tract  {tractus  cere- 
bro-cortico-pontalis temporalis,  Figs.  61,  93,  94  and  113)  extends 
from  the  temporal  lobe  through  the  inferior  lamina  (and  poste- 
rior part  of  the  superior  lamina)  of  the  internal  capsule  and  lateral 
one-fifth  of  the  basis  pedunculi  to  the  substantia  nigra  and  the 
16 


242 


THE   CEREBRUM 


nucleus  pontis;  but  according  to  Spitzka  some  of  its  fibers  end 
in  the  nuclei  of  motor  cerebral  nerves.  Thus  it  should  be  noted 
that,  with  the  exception  of  those  fibers  to  motor  nuclei  of  the 
cerebral  nerves,  each  of  the  three  tracts  above  mentioned,  viz., 
the  intermediate,  fronto-pontal  and  temporo-pontal,  constitutes 
a  segment  of  an  indirect  efferent  path  which  is  interrupted  in  the 
nucleus  pontis  and  then  continued  by  the  axones  of  that  nucleus 


Fig.  93. — A  horizontal  and  a  sagittal  section  of  the  left  cerebral  hemisphere 
showing  superior  and  inferior  laminae  of  internal  capsule.  Capsule  in  colors: 
red  tracts  are  descending;  blue  are  ascending;  and  purple  are  special  sense 
tracts. 

Blue,  Common  sensory  tracts.  Fr.  St.,  Frontal  stalk.  Par.  Stalk,  Parietal  stalk.  Ven- 
tral stalk.  Red,  Motor  tracts.  Fr.-P.  Tract,  Fronto-pontal  tract.  Pyr.  Tract,  Pyramidal 
tract.  Temp.-P.  Tr.,  Temporo-pontal  tract.  Interm.  Tract,  Intermediate  tract.  Purple, 
Special  sense  tracts.  Opt.  R.,  Occipito- thalamic  radiation.  Acust.  R.,  Temporo-thalamic 
radiation. 


through  the  brachium  pontis  of  the  cerebellum.  It  is  probable, 
though  not  surely  established,  that  the  fronto-pontal  and 
temporo-pontal  tracts  are  relayed  in  the  corpus  striatum  or  thala- 
mus, as  they  have  been  found  undegenerated  in  the  base  of  the 
peduncle  when  their  cortical  origins  were  destroyed  by  extensive 
lesions. 

The  pyramidal  tract    {tractus  cerehrospinalis    pyramidalis) 


PYRAMIDAL   TRACT  243 

(Figs.  93  and  94)  rises  in  the  anterior  central  gyrus  and  the  pre- 
central  part  of  the  paracentral  lobule.  It  is  composed  of  axones 
from  the  giant  pyramids  of  Betz  of  that  region.  Descending 
through  the  corona  radiata,  genu  and  anterior  two-thirds  of  the 
occipital  part  of  the  internal  capsule,  the  pyramidal  tract  com- 
prises the  middle  three-fifths  of  the  basis  pedunculi,  enters  into 
the  anterior  longitudinal  fibers  of  the  pons,  forms  the  pyramid  of 
the  medulla  and  the  anterior  and  lateral  pyramidal  tracts  of  the 
spinal  cord  (Figs.  61,  94, 113, 124 and  142).  The  fibers  of  the  py- 
ramidal tract,  with  a  few  exceptions,  cross  over  to  the  opposite 
side;  they  end  in  connection  with  the  motor  nuclei  of  cerebral 


Fig.  94. — Diagram  of  right  internal  capsule  in  colors.     (Original.) 
Red,  motor;  blue,  common  sensory;  purple,  special  sensory. 

and  spinal  nerves.  Fibers  enter  the  nucleus  of  the  trochlear  (or 
fourth)  nerve  chiefly  on  the  same  side,  and  a  few  descend  to  the 
motor  nuclei  of  other  cerebral  nerves  and  to  the  gray  matter  in 
the  spinal  cord  without  decussation;  all  other  pyramidal  fibers 
terminate  on  the  side  opposite  to  their  origin.  The  fibers  from 
the  lower  one- third  of  the  anterior  central  gyrus,  which  go  to  the 
motor  nuclei  of  the  cerebral  nerves,  to  a  large  extent  leave  the 
pyramidal  tract  high  up  in  the  peduncle  and  run  for  some  dis- 
tance through  the  medial  portion  of  the  fillet;  they  constitute 
Bechterew's  accessory  lemniscus.  This  accessory  fillet  has  been 
recently  traced  by  Flechsig. 


244  THE    CEREBRUM 

Head  and  Neck  Fibers  (Figs.  93,  147  and  148). — Those  fibers 
of  the  pyramidal  tract  which  end  in  the  nuclei  of  the  cerebral 
and  the  upper  four  cervical  nerves  rise  in  the  lower  segment  of 
the  motor  area,  including  that  part  of  the  anterior  central 
gyrus  below  the  genu  inferius  of  the  central  sulcus.  They  run 
through  the  genu  of  the  internal  capsule  to  the  peduncle  and 
then  both  through  the  accessory  fillet  and  the  inner  portion 
of  the  middle  three-fifths  of  the  basis  pedunculi.  Upper 
Extremity  Fibers  (Figs.  93  and  147). — The  fibers  of  the  py- 
ramidal tract  that  end  in  the  cervical  part  of  the  spinal  cord,  and 
through  it  innervate  the  muscles  of  the  upper  extremity,  take 
their  origin  from  that  part  of  the  anterior  central  gyrus  adjacent 
to  the  foot  of  the  middle  frontal  gyrus;  their  origin  lies  between 
meridians  which  intersect  the  central  sulcus  at  the  genu  in- 
ferius and  the  genu  superius,  respectively.  These  fibers  run 
through  the  pars  occipitalis  of  the  internal  capsule  just  behind 
the  genu,  and  through  the  basis  pedunculi  immediately  lateral 
to  the  head  and  neck  fibers.  Those  fibers  which  innervate  the 
muscles  of  the  thumb,  fingers  and  hand,  rise  lowest  down  in 
the  arm  area  of  the  cortex  and  occupy  the  posterior  part  of  the 
arm  bundle  in  the  internal  capsule  and  the  lateral  part  of  it  in 
the  peduncle.  The  fibers  which  control  the  shoulder  muscles 
rise  in  the  upper  part  of  the  cortical  area  and  form  the  anterior 
and  medial  part  of  the  arm  bundle  in  the  capsula  interna  and 
basis  pedunculi,  respectively;  while  the  wrist,  forearm,  elbow 
and  arm  are  innervated  by  means  of  fibers  which  are  inter- 
mediate in  both  origin  and  course.  Trunk  Fibers. — The  trunk 
fibers  of  the  pyramidal  tract  rise  in  that  projection  of  the  an- 
terior central  gyms  which  is  situated  just  above  the  genu 
superius  of  the  central  sulcus.  In  the  internal  capsule,  the 
trunk  fibers  run  just  behind  those  to  the  fingers  and  just  lateral 
to  them  in  the  basis  pedunculi.     Lower  Extremity  Fibers  (Figs. 

Description  to  Fig.  95. 

a,  a.  Motor  cells  of  cerebral  cortex,  b,  b.  End-tufts  of  sensory  fibers  in  cortex,  c.  Nu- 
cleus of  funiculus  cuneatus,  showing  end-tufts  of  fibers  from  the  cord.  d.  Nucleus  of  funic- 
ulus gracilis,  containing  end-tufts  of  fibers  from  cord.  e.  Section  of  medulla  at  fillet  de- 
cussation, f.  Section  of  medulla  at  pyramidal  decussation,  g,  g.  Motorial  end-plates. 
h.  Section  of  cervical  cord,  showing  terminations  of  fibers  of  anterior  and  lateral  pyramidal 
tract,  i,  i.  Spinal  ganglia,  j,  k.  Short  sensory  fibers.  1.  Long  sensory  fibers.  m,  m,  m. 
Sensory  end-organs,     n.  Section  of  lumbar  cord. 


MOTOR  AND   MUSCLE   SENSE   PATHS 


245 


Fig.  95. — A  diagram  showing  motor  and  sensory  paths;  motor  red,  sensory  blue. 

(After  Gordinier.) 


246  THE    CEREBRUM 

93  and  147). — A  large  number  of  the  pyramidal  fibers  terminate 
in  the  lumbar  enlargement  of  the  spinal  cord  and  carry  impulses 
to  the  nerves  of  the  lower  extremity.  They  originate  in  the 
upper  fourth  of  the  anterior  central  gyrus  and  in  the  paracentral 
lobule.  The  hip  fibers  rise  farthest  downward  and  the  toe 
fibers  farthest  upward,  immediately  in  front  of  the  sulcus 
centralis.  The  fibers  have  the  same  relative  position  in  the 
internal  capsule;  in  the  base  of  the  peduncle  the  hip  fibers  are 
medial  and  the  toe  fibers  lateral.  Fibers  which  innervate  the 
muscles  of  the  thigh,  leg  and  small  toes  have  this  same  relative 
position  and  order  between  the  hip  and  great  toe  fibers  both  in 
their  cortical  origin  and  in  their  course  through  the  internal 
capsule  and  basis  pedunculi. 

There  are  other  corticifugal  fibers  in  the  internal  capsule,  viz., 
some  within  the  occipito-thalamic  and  temporo-thalamic  radia- 
tions (Figs.  93  and  94)  and  others  running  from  the  static, 
olfactory,  gustatory  and  common  sensory  areas  of  the  cortex; 
but  these  fibers  are  probably  reflex  in  function  and  do  not 
properly  belong  to  the  projection  group.  They  are  axones  of 
the  large  pyramids  of  the  cortex,  but  not  of  the  giant  pyramids 
of  Betz.     The  latter  form  only  the  pyramidal  tract. 

Several  bundles  of  descending  fibers  are  found  in  the  teg- 
mentum and  tectum,  namely,  the  tecto-spinal,  reticulo-spinal, 
tecto-cerebellar,  dorsal  longitudinal  of  Schiitz,  thalamo-olivary, 
thalamo- spinal  and  rubro-spinal — all  belonging  to  reflex,  co- 
ordinating mechanisms;  and  the  mesencephalic  root  of  the 
trigeminal  nerve,  whose  function  is  not  positively  determined. 
With  these  exceptions  the  tegmentum  is  ascending  in  direction 
and  sensory  in  function. 

Destruction  by  clot  or  tumor,  or  otherwise,  of  any  of  the  above 
divisions  of  the  pyramidal  tract  causes  upper  segment  paralysis 
Qf  the  particular  muscles  innervated  through  that  tract,  the 
muscles  being  spastic  and  the  reflexes  increased. 

SENSORY  OR  CORTICIPETAL  PROJECTION  FffiERS 

The  sensory  or  corticipetal  projection  fibers  of  the  tegmentum 
comprise  the  medial,  superior  and  lateral  fillets;  the  spino- 


OLFACTORY   FASCICULI  247 

thalamic  tract;  the  brachium  conjunctivum  of  the  cerebellum; 
a  part  of  the  medial  longitudinal  bundle;  and  certain  other 
ascending  fibers  of  the  formatio  reticularis.  Excepting  a 
small  number  of  fibers,  all  these  bundles  terminate  in  the  basal 
ganglia;  but  the  paths  of  conduction  are  continued  through  the 
internal  capsule.  The  medial  fillet  carries  impressions  of  the 
tactile  and  the  muscular  senses;  the  spino-thalamic  tract  con- 
ducts tactile,  pain  and  temperature  impulses;  while  all  varieties 
of  common  sensory  impulses  may  be  carried  by  the  brachium 
conjunctivum  cerebelli,  its  chief  function  appears  to  be  the  con- 
duction of  coordinating  impulses  to  the  red  nucleus  and  thala- 
mus. Chiefly  through  these  three  tracts,  common  sensory 
impressions  arrive  in  the  lateral  nucleus  of  the  thalamus.  In 
the  capsula  interna  the  corticipetal  projection  fibers  constitute 
the  cortical  fillet  and  the  optic,  acustic  and  gustatory  radiations. 
The  former  end  in  the  somaesthetic  area  of  the  cerebral  cortex, 
the  latter  in  the  visual,  auditory  and  gustatory  cortex. 

The  olfactory  projection  fibers  are  contained  neither  in  the 
tegmentum  nor  in  the  internal  capsule.  They  proceed  from  the 
nasal  mucous  membrane  to  the  olfactory  bulb,  through  the 
olfactory  tract  and  its  striae,  directly  to  the  cerebral  cortex. 
The  afferent  olfactory  neurones  are  of  three  orders,  first, 
second  and  third.  The  first  order  neurones  are  the  olfactory 
nerve  neurones,  which  reach  from  the  nasal  mucous  membrane 
to  the  stratum  glomerulosum  of  the  bulb.  The  second  order 
are  the  mitral  and  brush  neurones  whose  dendrites  receive  the 
first  order  neurones  and  whose  axones  form  the  olfactory  tract; 
they  terminate  in  the  cortex  of  the  tract,  in  the  olfactory  tri- 
angle, the  anterior  perforated  substance  and  the  septum  pellu- 
cidum,  where  the  bodies  of  the  third  order  neurones  are  lo- 
cated.    The  third  order  neurones  form  the  olfactory  strict: 

The  lateral  stria  rises  in  the  olfactory  triangle  and  ends  in 
the  uncus  hippocampi. 

The  intermediate  stria  is  made  up  of  four  bundles — the 
olfacto-hippocampal  of  the  fornix  rises  in  the  olfactory  triangle, 
anterior  perforated  substance  and  septum  pellucidum  and  ter- 
minates in  the  hippocampal  formation;  the  olfacto-amygdalate 


248  THE    CEREBRUM 

bundle  rises  in  the  anterior  perforated  substance  and  septum 
pellucidum  and,  partially  decussating  through  the  anterior 
commissure,  runs  through  the  stria  terminalis  to  the  nucleus 
amygdalae.  As  it  ascends  some  of  its  fibers  end  in  the  anterior 
nucleus  of  the  thalamus.  The  olfacto-habenular  fasciculus 
and  the  olfacto-mesen cephalic  fasciculus  form  a  part  of  the 
intermediate  stria;  they  are  described  below  with  the  reflex 
olfactory  neurones. 

The  medial  stria,  the  stria  Lancisii,  originates  in  the  olfactory 
triangle  and  runs,  perhaps  with  several  relays,  through  the 
subcallosal  and  supracallosal  gyri,  the  fasciola  cinerea  and 
gyrus  subspleniahs,  and  the  dentate  fascia  to  the  hippocampal 
formation  (Retzius,  Villiger,  Elliot  Smith,  etc.). 

Efferent  Reflex  Olfactory  Neurones. — Though  these  neurones 
are  associative,  they  belong  to  efferent  chains  that  reach  to  motor 
nuclei  and  form  intermediate  links  of  reflex  arcs;  hence,  they 
may  be  considered  in  this  place. 

Fornix. — The  hip pocampo-mammillary  fasciculus  rises  in  the 
hippocampus,  hippocampal  gyrus,  dentate  fascia  and  gyrus 
cinguli  (fibrae  perforantes)  and  terminates  in  the  medial  nucleus 
of  the  mammillary  body,  chiefly  on  the  same  side  but  partly  on 
the  opposite  side.  The  hippocampo-hahenular fasciculus  has  the 
same  origin.  It  runs  through  the  crus  and  body  of  the  fornix 
with  the  former  bundle  to  the  columna  fornicis;  there  it  turns 
backward  and  proceeds  through  the  stria  medullaris  thalami 
and  commissura  habenularum  to  the  opposite  nucleus  haben- 
ulae — a  few  fibers  end  on  the  same  side. 

The  olfacto-habenular  fasciculus  originates  in  the  anterior 
perforated  substance  and  septum  pellucidum;  ascending  to  the 
stria  medullaris  thalami  it  runs  through  that  and  the  com- 
missura habenularum  to  the  opposite  nucleus  habenulas.  Some 
of  its  fibers  terminate  in  the  tectum,  especially  in  superior 
colliculi. 

Olfacto-mesencephalic  Fasciculus  (Basal  Bundle  of  Wallen- 
berg).— This  bundle  rises  in  the  cortex  of  the  olfactory  tract. 
It  terminates  in  the  tuber  cinereum,  mammillary  body,  teg- 
mentum of  mid-brain,  pons,  medulla  and  cord. 


CORTICAL   FILLET 

The  fasciculus  mammillaris  princeps  with  its  two  divisions 
the  mammillo-thalamic  and  mammillo-tegmental  fasciculi  (p. 
86);  the  pedunculus  corporis  mammillaris  (p.  86);  and  the 
hahenulo -peduncular  fasciculus  (p.  147,  222)  are  described  on 
the  pages  indicated. 

The  inter pedunculo-tegmental  fasciculus  rises  from  the  inter- 
peduncular nucleus  (ganglion)  and  terminates  in  the  stratum 
griseum  centrale,  the  nucleus  tegmenti  dorsalis  and  nucleus  teg- 
menti  profundus,  where  the  dorsal  longitudinal  bundle  of 
Schiitz  and  the  reticulo-spinal  tracts  arise  and  continue  to  vari- 
ous motor  nuclei. 

The  exact  origin  of  the  cortical  fillet  (Figs.  93  and  94)  has 
not  been  entirely  determined,  but  it  is  known  to  rise  chiefly 
in  the  lateral  nucleus  of  the  thalamus.  The  ventral  stalk  of  the 
thalamus  (Fig.  93)  runs  through  the  internal  capsule  in  the 
inferior  lamina.  Its  afferent  fibers  end  in  the  globus  pallidus. 
The  ventral  stalk  of  the  thalamus  can  no  longer  be  considered 
a  part  of  the  cortical  fillet;  as  its  afferent  fibers  end  in  globus 
pallidus  which  has  no  direct  connection  with  the  cortex  (see 
p.  218).  From  the  anterior  end  of  the  thalamus  streams  a 
great  pencil  of  fibers,  called  the  frontal  stalk  (Fig.  93).  It 
mingles  to  a  small  extent  with  the  fibers  of  the  pyramidal  tract, 
but  runs  chiefly  through  the  frontal  part  of  the  internal  capsule. 
Its  termination  is  in  the  caudate  nucleus  and  the  posterior  and 
middle  parts  of  the  three  frontal  gyri. 

The  parietal  stalk  issues  from  the  lateral  surface  of  the  thala- 
mus higher  up  than  the  ventral  stalk  and  mingles  with  the  py- 
ramidal fibers  in  the  superior  lamina  of  the  internal  capsule.  Its 
location  is  principally  in  the  posterior  third  of  the  occipital  part 
of  the  capsule  (Figs.  93  and  94).  Its  sensory  fibers  terminate  in 
the  posterior  central  gyrus  and  the  contiguous  part  of  the 
paracentral  gyrus;  these  are  small  and  medium-sized  fibers 
(Sachs).  A  greater  number  of  fibers  (of  medium  caliber  with  a 
few  large  and  small  fibers  interspersed)  end  in  front  of  the 
central  sulcus — in  the  fronto-parietal  operculum,  the  anterior 
central  and  superior  frontal  gyri  and  the  middle  of  the  gyrus 
cinguli.    The  fibers  of  this  larger  group  are  not  sensory,  as 


250  THE    CEREBRUM 

their  impulses  do  not  excite  sensations;  they  have  a  rejlex  or 
automatic  function,  and  probably  exert  a  controlling  influence 
over  motor  discharges  from  the  cortex.  The  sensory  fibers  of  the 
parietal  stalk  carry  impulses  to  the  receptive  sensory 
cortex,  where  the  proper  sensations  are  evoked.  According  to 
Head  and  Holmes,  they  form  five  functional  tracts  which  trans- 
mit all  kinds  of  common  sensory  impulses  except  those  of  pain 
and  pleasure  (see  p.  225). 

Three  special  sense  fasciculi  traverse  the  internal  capsule, 
the  gustatory,  the  optic  and  the  acustic  or  auditory.  Recently, 
the  gustatory  fasciculus  has  been  traced  by  Otto  May  and  Sir 
Victor  Horsley  (Brain,  Vol.  33,  p.  186).  It  rises  in  the  nu- 
cleus of  the  solitary  tract  (nucleus  of  Nageotte).  Ascending 
beside  the  central  gray  substance  of  the  mid-brain,  dorsal  and 
lateral  to  the  medial  longitudinal  bundle,  it  enters  the  internal 
medullary  lamina  of  the  thalamus  and  terminates  in  the  dorsal 
third  of  the  nucleus  laterahs.  The  gustatory  radiation  of  the 
internal  capsule,  probably  located  between  the  optic  radiation 
and  the  parietal  stalk  of  the  thalamus,  continues  the  taste  path 
from  thalamus  to  cortex.  Auditory  impulses  run  through 
the  lateral  fillet  and  the  brachium  inferius  to  the  medial  genicu- 
late body;  while  optic  impulses  run  directly  to  the  lateral  genicu- 
late body  and  the  pulvinar  without  passing  through  the  mid- 
brain at  all.  Within  the  internal  capsule  the  gustatory  tract 
cannot  positively  be  located;  but  the  acustic  and  visual  paths 
are  well  known. 

The  acustic  radiation  (Figs  93  and  74)  continues  the  auditory 
path  from  the  medial  geniculate  body  through  the  retrolenti- 
form  part  of  the  internal  capsule,  to  the  transverse  temporal 
gyri  and  the  third  and  fourth  fifths  of  the  superior  temporal 
gyrus  (Barker).  Interruption  of  these  fibers  produces  deafness 
in  the  opposite  ear,  which  is  complete  because  the  acustic  path 
above  the  inferior  quadrigeminal  colliculi  is  wholly  crossed. 
There  are  some  corticifugal  temporo-thalamic  fibers  in  the 
acustic  radiation;  they  are  probably  reflex  in  function. 

The  optic  radiation  (Figs.  49,  75,  93  and  94)  rises  in  the  lateral 
geniculate  body  and  in  the  pulvinar  of  the  thalamus.     It  con- 


COMMISSURES  25 1 

tinues  the  visual  conduction  path  through  the  retrolentiform 
region  of  the  internal  capsule  to  the  cortex  of  the  lingual  and 
cuneate  gyri.  Half-blindness  in  the  same  side  of  both  retinae 
results  from  section  of  the  optic  radiation.  The  corticifugal 
occipito-thalamic  fibers  in  the  optic  radiation  are  beHeved  by 
Campbell  to  be  axones  of  the  solitary  giant  cells  (Meynert's) 
in  the  occipital  cortex.  They  run  through  the  lateral  geniculate 
body  and  brachium  superius  to  the  superior  colliculus  of  the 
corpora  quadrigemina,  where  they  end  in  contact  with  the  neu- 
rones of  the  anterior  tecto-spinal  bundle.  Their  function  is 
reflex. 

n.    COMMISSURAL  FIBERS 

They  connect  opposite  sides  of  the  cerebrum  and,  like  the  pro- 
jection fibers,  are  continuous  with  the  radiations  of  Meynert. 
They  are  contained  chiefly  in  the  corpus  callosum,  the  anterior 
commissure,  and  the  commissura  hippocampi;  but  are  also 
found  in  the  posterior  commissure,  commissura  habenularum, 
inferior  (Gudden's)  and  superior  (Meynert's)  commissures. 

The  corpus  callosum,  as  already  described,  is  the  great  link 
between  the  cerebral  hemispheres  (Figs.  33,  42  and  96).  Its 
fibers  connect  both  similar  and  dissimilar  parts  of  the  cortices; 
within  the  hemisphere,  they  form  a  prominent  radiation,  called 
the  radiatio  corporis  callosi.  Valkenburg  has  confirmed  in  man 
the  observation  of  Beevor  (1891)  upon  the  marmoset,  that  the 
corpus  callosum  contains  no  fibers  from  the  striate  (visual)  cor- 
tex, though  the  psychic  visual  cortex  contributes  fibers  to  it. 
Valkenburg  traced  an  abundant  connection  of  the  anterior  cen- 
tral gyrus  with  both  central  gyri  of  the  opposite  side  (Brain,  Vol. 
36).  This  important  contribution  appears  to  explain  the  gen- 
eral epileptic  convulsion  due  to  unilateral  irritation,  and  the  one 
well-known  symptom  of  callosal  lesion,  viz.,  left-sided  apraxia. 
J.  Levy-Valensi  claims  that  lesions  of  the  corpus  callosum  in  man 
also  cause  reduction  of  association  of  ideas  and  weakening  of 
memory;  and,  sometimes,  change  in  character  and  bilateral 
motor  disturbance.  The  views  of  Levy-Valensi  (Brain,  Vol.  34) 
afford  some  support  to  the  endeavor  of  Spitzka  to  establish  a 


252 


THE   CEREBRUM 


direct  relation  between  the  size  of  the  corpus  callosum  and  the 
mental  power  of  the  individual.  It  is  the  corpus  callosum, 
chiefly,  that  makes  it  possible  for  the  two  hemispheres  of  the 
cerebrum  to  act  together  as  one  organ.  Philogenetically,  it  is  of 
recent  development,  since  it  is  not  found  below  mammals.  It 
is  developed  in  the  lamina  terminalis  just  above  the  anterior 


Fig.  96. — Transverse  section  of  cerebrum,  cutting  corpus  callosum,  anterior 
commissure  and  optic  chiasma.  Viewed  from  front.  Commissural  fibers. 
{Morris's  Anatomy  after  Toldt.) 

a.  Caudate  nucleus  (head),  b.  Internal  capsule  (frontal  portion).  Lentiform  nucleus; 
c.  Putamen,  d.  Globus  pallidus.  e.  Medullary  lamina,  f.  External  capsule,  g.  Claus- 
trum.  h.  Vena  terminalis.  i.  Interventricular  foramen  (Monroi).  j.  Anterior  perforated 
substance,  k.  Uncus.  1.  Anterior  commissure,  m.  Longitudinal  fissure,  n.  Corpus 
callosum.  o.  Anterior  horn  of  lateral  ventricle,  p.  Chorioid  plexus  of  lateral  ventricle. 
<1.  Septum  pellucidum.  r.  Columns  of  fornix,  s.  Lateral  fissure  (Sylvii).  t.  Gyri  of 
insula,  u.  Optic  recess,  v.  Optic  tract,  w.  Optic  chiasma.  x.  Inferior 
(Guddeni). 


commissure 


neuropore;  the  anterior  commissure  is  thrown  across  just  below 
the  neuropore  (Johnston). 

The  anterior  commissure  (Figs.  33,  50  and  96)  joins  the 
opposite  temporal  and  occipital  lobes  together  {pars  occipito- 
temporalis)j  the  limbic  lobes  with  the  contra-lateral  olfactory 
tracts,  and  the  olfactory  tracts  with  each  other  {pars  olfactoria) . 


ASSOCIATION   FIBERS 


253 


It  is  supplementary  to  the  corpus  callosum  and  associates  re- 
gions not  joined  by  the  great  commissure,  especially  the  cortex  of 
the  tentorial  areas  of  the  cerebral  hemispheres.  In  size  it  va- 
ries inversely  as  the  corpus  callosum.  Its  importance  diminishes 
with  the  appearance  of  the  corpus  callosum  in  the  lower  mam- 
malia and  it  continues  to  decrease  as  the  higher  forms  are 
approached.  Below  mammals  it  is  said  to  be  the  most  impor- 
tant connecting  link  between  the  hemispheres  and  is  philogen- 
etically  very  old  (see  p.  133). 

The  commissura  hippocampij  the  lyre  (Fig.  47),  unites  the 
hippocampal  gyrus,  dentate  fascia,  and  the  hippocampus  with 
their  fellows  of  the  opposite  side.  This  is  the  commissure  of  the 
pyriform  lobes,  the  cortical  areas  of  smell. 

The  lamina  terminalis  becomes  thickened  by  the  invasion  of 
gray  substance  due  to  the  fusion  of  the  medial  olfactory  nuclei. 
That  thickening  Elliot  Smith  designated  the  ^^precommissural 
bodyJ^  The  precommissural  body  forms  the  anterior  wall  and  a 
part  of  the  floor  of  the  median  ventricle  of  the  telencephalon, 
the  aula.  According  to  Johnston  it  pushes  up  into  the  supra- 
neuroporic  lamina  and  constitutes  the  bed  for  corpus  callosum^ 
commissura  hippocampi  and  corpus  Jornicis.  The  part  of  the 
precommissural  body  inclosed  by  the  three  structures  just 
named  forms  the  septum  pellucidum. 

m.    ASSOCIATION  FIBERS 

These  fibers  remain  on  the  same  side  and  connect  parts  of  the 
same  hemisphere.  They  are  situated  within  or  beneath  the  cor- 
tex, the  various  parts  of  which  they  serve  to  unite.  Associa- 
tion fibers  become  medullated  and  actively  functional  only  as 
mental  effort  and  education  gradually  develop  them.  So  far  as 
the  brain  is  concerned  education  consists,  jirst^  in  the  develop- 
ment of  the  functional  centers  of  the  brain;  and,  second,  in  the 
establishment  of  lines  of  rapid  communication  between  them. 

The  short  association  fibers  are  the  more  numerous  and  are 
very  important.  They  unite  contiguous  parts  of  the  same  gy- 
rus and  associate  together  adjacent  gyri.     They  are  intralobar. 


254 


THE    CEREBRUM 


In  direction  they  comprise  arcuate  and  tangential  fibers;  and 
they  are  intracortical  and  subcortical^  in  position.  Every  zone  of 
the  cerebral  cortex  contains  association  fibers,  from  the  felt- 
work  of  Kaes  to  the  stratum  zonale.  But  they  are  found  chiefly 
(i)  in  the  radiary  zone  and  adjacent  part  of  the  supraradiary 
zone,  along  the  lines  of  Baillarger  (Fig.  80) ;  and  (2)  in  the  zonal 
layer  (Figs.  84  and  85).  The  deeper  of  these  fibers  are  con- 
tinuous with  the  radiations  of  Meynert  and  probably  do  not 
belong  to  the  short  association  fibers,  if  associative  at  all  (they 


Superior  longitudinal  fasciculus 


Uncinate  part  o 
occipito-frontal 
fasciculus 


Inferior  longitudial  fasc.  of  inferior  occipito- 
frontal fasc. 

Fig.  97. — ^Long  association  tracts  as  shown  on  the  convex  surface  of  the 
cerebral  hemisphere.  Superior  longitudinal  fasciculus;  inferior  occipito-frontal 
fasciculus,  embracing  uncinate  fasciculus  and  the  inferior  longitudinal  fasciculus. 


are  corticipetal  fibers);  the  more  superficial  intersect  the  ra- 
diations at  right  angles  and  are  truly  associative  in  function. 
The  associative  fibers  of  Meynert  are  compacted  together  by 
pressure  in  the  walls  and  floor  of  the  sulci.  In  the  crown  of  a 
gyrus  they  are  scattered.  Their  exact  origins  are  not  yet 
worked  out;  but  they  are  probably  the  horizontal  processes  of 
cells  in  the  second  to  sixth  layers.  (2)  The  association  fibers  of 
the  plexiform  layer  of  the  cortex,  which  constitute  the  stratum 
zonale  (Fig.  84),  are  quite  short;  they  join  together  immediately 


LONG   ASSOCIATION   FIBERS  255 

contiguous  parts  within  circumscribed  areas.  The  richness  of 
the  zonal  layer  of  fibers,  as  already  pointed  out  in  describing 
the  plexiform  layer  of  the  cortex,  varies  greatly  in  different 
regions,  being  best  developed  in  the  subiculum.  The  fibers 
comprising  the  zonal  layer  have  four  sources  of  origin:  (a)  The 
axones  and  dendrites  of  the  cells  of  Golgi  and  Cajal  in  the  plexi- 
form layer.  (6)  The  apical  dendrites  of  the  subjacent  pyra- 
mids, (c)  The  T-branched  axones  of  Martinotti's  cells,  {d) 
The  corticipetal  axones  which  terminate  in  the  superficial  layer 
of  the  cortex. 

The  short  association  fibers  are  almost  infinite  in  their  con- 
nections. They  connect  the  receptive  and  psychic  sensory 
areas,  and  their  interruption  on  the  left  side  causes  inability  to 
interpret  the  sensations,  agnosia,  called  mind-blindness,  mind- 
deafness,  stereagnosis,  etc.  Again,  those  short  fibers  also 
associate  the  psychic  with  the  psychic-motor,  and  the  psychic- 
motor  with  the  emissive-motor  centers.  In  this  manner  the 
writing  center  is  connected  with  the  motor  center  for  the  upper 
extremity,  and  the  speech  center  with  the  motor  centers  for 
the  lips,  tongue,  etc.:  breaking  of  the  former  connection  on 
the  left  side  destroys  ability  to  write,  agraphia;  and  aphasia 
results,  if  the  latter  connection  is  broken.  Besides  these  and 
many  other  connections  of  associated  centers,  the  short  fibers 
join  together  the  various  parts  of  each  cortical  area. 

The  long  association  fibers  (Figs.  97-100)  are  collected 
into  bundles.  They  rise  from  the  pyramidal,  the  polymorphous 
and  the  fusiform  layers  of  the  cerebral  cortex  (Cajal),  and  are 
axones.  Proceeding  out  of  the  lobe  in  which  they  rise,  being 
interlobar,  they  dip  down  into  the  centrum  semiovale  and  arbor- 
ize about  neurones  in  more  or  less  distant  parts  of  the  cortex. 
Among  the  best  known  are  the  following  bundles: 

I.  The  cingulum  of  the  gyrus  fornicatus  (Fig.  98)  is  a  bundle 
of  fibers  in  that  gyrus  which  almost  entirely  encircles  the  corpus 
callosum.  It  extends  from  the  anterior  perforated  substance 
through  the  gyrus  cinguli  and  hippocampal  gyrus,  to  the  uncus 
and  temporal  pole.  The  fibers,  which  form  several  systems, 
radiate  from  the  limbic  lobe  to  the  surrounding  gyri  of  the 


256 


THE    CEREBRUM 


medial  surface;  they  join  the  limbic  lobe  with  the  superior 
frontal,  the  paracentral,  the  precuneate,  the  cuneate,  the  lingual 
and  the  fusiform  gyri.  The  cingulum  does  not  form  a  con- 
tinuous strand  through  the  gyrus  fornicatus;  hence,  the 
name  fornix  periphericus,  given  it  by  Arnold,  is  not  entirely 
appropriate. 

Like  the  two  following  bundles  it  establishes  associations 
for  the  sense  of  smell. 

2 .  The  Fornix  (Figs.  5 1  and  5  2) . — In  each  lateral  half  of  the  f  or- 


Cingulum 


Perpendic- 
ular fascic- 
ulus 


Inferior  longitudinal  fasciculus 
Interior  part  of  cingulum 

Fig.  98. — Long  association  tracts  as  shown  on  the  medial  surface  of  the  cerebral 
hemisphere.  Cingulum,  inferior  longitudinal  bundle,  and  perpendicular 
fasciculus. 


nix  there  are  four  fasciculi :  (a)  The  olfacto-hippocampal fasciculus, 
which  rises  in  the  olfactory  triangle,  anterior  perforated  sub- 
stance and  septum  pellucidum  and  terminates  in  the  hippo- 
campus and  uncus.  There  are  two  efferent  fasciculi,  of  reflex 
function,  in  the  fornix,  which  associate  the  hippocampal  forma- 
tion with  the  mammillary  and  habenular  nuclei;  {b)  the  hippo- 
campo-mammillary  fasciculus  and  (c)  the  hippocampo-habenular 
fasciculus;  these  rise  in  the  hippocampal  formation,  and  in  the 
supracallosal  and  cingulate  gyri;  their  terminations  are  indi- 


FASCICULUS   OCCIPITO-FRONTALIS 


257 


cated  by  their  names.  The  fibers  froiri  the  supracallosal  and 
cingulate  gyri  pierce  the  corpus  callosum  as  the  fibrce  per/or  antes 
of  the  fornix  longus  (Forel).  All  these  may  be  considered 
associative  in  function,  though  they  belong  to  afferent  and  effer- 
ent paths  (see  p.  247).  {d)  The  commissural  bundle  of  the 
fornix  connects  the  hippocampal  formations;  it  is  the  commissura 
hippocampi  (p.  108). 

3 .  Fasciculus  Occipito-frontalis  Inferior. — The  work  of  E.  J. 
Curran  has  simpHfied  certain  systems  of  association  fibers  of 


Super  or  occipito-f rental  fasciculus 


Tapetum 


Inferior  occip- 
ito-f  rental 
fasciculus 


Inferior  occipito-f rental  fasciculus 
Uncinate  fasciculus 
Fig.  99. — An  oblique  longitudinal  section  of  the  cerebral  hemisphere  cutting  the 
superior  occipito-f rontal  fasciculus  and  the  inferior  occipito-f rontal  fasciculus. 

the  cerebrum.  Curran  shows  that  the  uncinate  and  inferior 
longitudinal  fasciculi,  formerly  considered  separate  systems, 
are  but  parts  of  one  greater  system  extending  through  the  basal 
portion  of  the  hemisphere  from  the  frontal  to  the  occipital  pole. 
This  inferior  occipito-frontal  fasciculus,  in  its  middle  part,  is 
compact  and  lies  below  the  putamen  and  claustrum,  in  the  base 
of  the  external  capsule;  in  front,  it  radiates  to  the  orbital  and 
inferior  frontal  gyri;  it  establishes  connections  with  the  temporal 
and  uncinate  gyri  in  the  middle  region;  and,  posteriorly,  it 
runs  lateral  to  the  optic  radiation  to  reach  the  fusiform,  lingual, 
17 


258 


THE    CEREBRUM 


cuneate  and  occipital  gyri  (Jour.  Comp.  Neurol.  &  Psychol., 
Vol.  1.9).  The  function  of  this  bundle  is  uncertain.  The  fact 
that  its  occipital  part  is  well  developed  in  the  chimpanzee  and 
orang,  but  not  present  in  the  macaque  monkey  (Ferrier  and 


Turner)  throws  little  light  upon  it.  The  part  of  the  inferior 
occipito-frontal  fasciculus  that  arches  over  the  lateral  fissure, 
connecting  the  frontal  with  the  temporal  and  limbic  lobes,  is, 
the  fasciculus  uncinatus  of  the  older  descriptions,  while  that 


ASSOCIATION  TRACTS  259 

part  which  joins  the  temporal  pole  and  gyri  with  the  gyri  about 
the  occipital  pole  constitutes  the  fasciculus  longitudinalis  in- 
ferior, as  described  in  former  editions  of  this  book;  the  deeper 
and  longer  fibers,  which  reach  the  whole  length  of  the  hemi- 
sphere and  connect  the  uncinate  and  inferior  longitudinal 
fasciculi  into  one  system,  were  first  demonstrated  by  Curran. 
The  tracing  was  accomplished  by  blunt  dissection,  an  old-time 
method  revived  and  successfully  employed  by  Hubertus 
J.  H.  Hoeve  (Figs.  99  and  100). 

4.  The  superior  longitudinal  fasciculus  {fasciculus  longitud- 
inalis superior,  Fig.  97)  is  a  sagittal  bundle  located  beneath 
the  convex  surface  of  the  hemisphere,  just  above  the  posterior 
ramus  of  the  lateral  fissure  of  the  cerebrum.  According  to 
Cunningham,  it  runs  just  above  and  lateral  to  the  putamen  of 
the  lentiform  nucleus,  external  to  the  base  of  the  corona  radiata. 
It  runs  through  the  summit  of  the  external  capsule,  as  the  infe- 
rior occipito-frontal  fasciculus  runs  through  the  base.  Its 
fibers  diverge  at  the  posterior  end  of  the  lateral  fissure  and  ra- 
diate into  the  parietal,  occipital  and  temporal  cortex:  some  of 
them,  arching  around  that  fissure,  run  as  far  forward  as  the 
temporal  pole.  The  superior  longitudinal  bundle  joins  the 
frontal  cortex  with  the  parietal,  occipital  and  the  external  tem- 
poral. It  thus  associates  the  psychic  auditory  and  visual  cen- 
ters with  the  motor  speech  center;  hence  motor  aphasia  is  the 
result  of  its  interruption. 

5.  The  Fasciculus  Occipito-frontalis  Superior  (Foreli). — This 
is  a  large  bundle  of  fibers  formerly  regarded  as  a  part  of  the 
corpus  callosum  (Fig.  99).  It  is  situated  below  the  corpus 
callosum  and,  in  equatorial  sections  of  the  brain,  is  found  in  the 
angle  formed  between  the  callosum  and  the  internal  capsule, 
just  external  to  the  lateral  ventricle.  It  extends  from  the  cor- 
tex of  every  part  of  the  frontal  lobe  to  the  cortex  of  the  convex 
surface  and  lateral  border  of  the  occipital  lobe.  Posteriorly, 
the  fibers  diverge  to  form  a  fan-like  sheet  in  which  there  is  an 
intermingling  of  fibers  from  the  corpus  callosum  (Cunningham); 
and  that  sheet  enters  into  the  external  boundary  of  the  inferior 
horn  of  the  lateral  ventricle  and  into  the  floor,  lateral  wall  and 


26o  THE    CEREBRUM 

roof  of  the  posterior  horn,  hence  the  synonym,  tapetum.  The 
tapetum  is  lined  by  the  ventricular  ependyma  and  is  separated 
from  the  inferior  longitudinal  bundle  by  the  optic  radiation. 
Its  particular  function  is  unknown.  It  has  been  recently 
suggested  that  the  fibers  of  this  bundle  are  projection  fibers 
connected  with  the  corpus  striatum;  but  this  is  so  at  variance 
with  the  findings  of  Kinnier  Wilson  in  apes  that  it  should  not  be 
accepted  without  confirmation. 

6.  The  Perpendicular  Fasciculus  {Fasciculus  Perpendicularis, 
Fig.  98). — This  is  a  very  broad  vertical  system  located  just  in 
front  of  the  occipital  pole.  It  extends  from  the  inferor  parietal 
and  superior  occipital  gyri,  above,  down  to  the  middle  and  in- 
ferior temporal,  the  lateral  occipital  and  the  fusiform  gyri.  It 
is  often  classed  with  the  short  association  fibers.  Its  function  is 
doubtful. 

The  fore-brain  is  best  adapted  to  the  development  of  the 
intellectual  faculties,  as  Johnston  has  pointed  out: 

1.  It  possesses  a  correlation  center  free  from  the  dominance  of  any  one 
set  of  impulses.  The  reduction  of  the  nervus  terminalis  to  a  functionless 
remnant  provides  this  indifferent  nucleus,  and  within  it  all  varieties  of 
impulses  from  every  part  of  the  body  may  meet  on  an  equality  and  interact 
upon  one  another. 

2.  The  fore-brain  is  farthest  removed  from  the  points  of  stimulation, 
being  connected  with  them  only  by  long  chains  of  three  or  more  neurones. 
The  long  arcs  connecting  it  with  the  periphery  remove  the  fore-brain  from 
the  field  of  simple  reflexes,  because  of  the  long  reaction  time  necessitated  by 
such  long  arcs.  They  also  winnow  out  the  impulses  at  each  synapsis  and 
at  each  successive  junction  of  the  afferent  and  efferent  limbs  of  the  various 
arcs;  so  that  only  the  more  powerful  impulses,  those  having  a  broad  general 
significance  to  the  organism,  and  the  impulses  for  which  the  way  is  opened 
by  expectant  attention  succeed  in  entering  the  correlation  centers  of  the 
fore- brain.  A  calm  interaction  and  balancing  of  impulses  and  a  rational 
response  are  thus  rendered  possible  in  the  fore-brain,  as  it  is  in  no  other  part  of 
the  brain.  These  correlation  centers  of  the  fore-brain,  which  develop  into  the 
in.diXVt\o\xsoxg2insoi  memory,  judgment2iiid.  reasoning,  diXt  the  full  fruition 
of  their  diminutive  primordia  laid  down  in  the  lowest  fishes  (Anat.  Rec, 
Vol.  4). 

Evolution  of  the  Brain. — In  the  very  simple  animal  forms  (as  the  coelen- 
terates)  the  nervous  sytem  is  represented  by  single  reflex  mechanisms. 
These  mechanisms  at  first  are  complete  in  a  single  sense-cell;  but   later 


EVOLUTION  OF  BRAIN 

they  are  formed  by  the  junction  of  an  afferent  and  an  efferent  neurone. 
They  are  perfected  and  elaborated  by  the  development  of  intermediate 
links  between  the  afferent  and  efferent  neurones,  and  the  reflex  mechanisms 
are  multiplied  with  little  or  no  interconnection  between  them;  hence 
invertebrates  are  reflex  organisms.  Vertebrates  present  a  series  of  seg- 
mental  reflex  arcs  in  the  neural  tube  which  become  correlated  with  each 
other,  step  by  step;  association  tracts  of  increasing  length  are  built  up  for 
this  purpose;  the  reflex  arcs  are  elongated  and  their  efferent  limbs  form  a 
common  motor  path  for  the  mechanism  of  locomotion.  Intersegmental 
correlation  progresses  in  complexity  toward  the  head  of  the  organims. 
With  this  progressive  process  the  correlation  neurones  establish  a  more 
general  connection  with  all  parts  of  the  organism,  the  impulses  received 
become  more  varied  and  the  reflex  mechanisms  assume  a  wider  and  more 
general  significance.  As  a  result,  a  correlation  center  of  great  importance 
is  built  up  in  the  posterior  nuclei  of  the  medulla  (Coghill).  The  progres- 
sively more  elaborate  intersegmental  correlations  of  the  cephalic  mechan- 
isms gradually  leads  to  local  hypertrophy  and  the  evolution  of  the  brain. 
The  elaboration  of  a  correlation  center  for  the  muscle  and  static  senses 
forms  the  cerebellum.  The  building  up  of  the  more  complex  and  extensive 
correlations,  the  correlations  that  connect  and  harmonize  all  the  nervous 
mechanisms  of  the  organism,  somatic  and  visceral,  forms  the  cerebrum 
with  its  massive  hemispheres.  The'  development  of  the  brain  is  largely 
determined  by  the  imperative  demands  of  food-getting  and  the  consequent 
formation  in  the  head  of  the  organs  of  special  sense  (J.  B.  Johnston). 


CHAPTER  IV 
THE  RHOMBENCEPHALON 
SECTION  I.    THE  CEREBELLUM 

The  rhombencephalon  is  composed  of  the  isthmus,  the  cere- 
helium,  the  pons  and  the  medulla  oblongata  (Figs.  20,  21,  and  33). 
It  is  the  lozenge-shaped  brain.  It  is  evolved  from  the  third 
primary  brain- vesicle;  therefore,  it  is  the  hind-brain.  In  con- 
trast with  the  cerebrum,  it  is  the  little-brain. 

The  narrow  connection  between  the  second  and  third  primary 
brain-vesicles  constitutes  the  isthmus  rhombencephali.  The 
isthmus  is  almost  without  length;  it  is  little  more  than  the  plane 
of  union  between  the  mid-brain  and  the  hind-brain.  Through 
the  isthmus  pass  the  various  tracts  to  and  from  the  cerebrum, 
contained  above  this  level  in  the  base  and  tegmentum  of  the 
peduncle ;  the  superior  end  of  the  fourth  ventricle  is  bounded  by 
it  and  from  its  dorsal  surface  the  trochlear  nerve  makes  its 
exit  from  the  brain. 

At  the  fourth  week  in  utero,  the  third  primary  brain-vesicle  is 
subdivided  into  two  secondary  vesicles,  the  metencephalon 
(above)  and  the  myelencephalon  (below) .  The  myelencephalon 
(marrow-brain)  is  the  embryonic  medulla  oblongata;  the  *meten- 
cephalon  develops  the  pons  and  cerebellum.  The  cerebellum  is 
the  dorsal  and  the  pons  the  ventral  part  of  the  metencephalon. 
The  preponderant  size  of  the  cerebellum  is  due  to  the  accumula- 
tion of  emigrant  cells  in  the  dorsal  zones  and  roof-plate  of  the 
metencephalon;  the  cells  are  derived  from  the  somatic  sensory 
column  of  the  medulla  in  the  region  of  the  rhomboid  lip  (Her- 
rick).  The  large  cerebellum  is  characteristic  of  man.  Its 
weight  is  140  grams  (5  ounces)  slightly  more  than  one-tenth  of 
the  whole  brain.  It  is  situated  in  the  posterior  fossa  of  the  skull, 
under  the  tentorium  cerebelli  and  dorsal  to  the  pons  and  medulla 

262 


FUNCTION   OF   CEREBELLUM  263 

oblongata.  Between  it  and  the  last  two  structures  is  enclosed 
the  fourth  ventricle.  The  cerebellum  is  distinguished  from  the 
cerebrum  by  its  stratification.  Its  surface  is  composed  of  gray 
substance,  the  cortex  {substantia  corticalis);  its  interior  is  white 
and  is  called  the  medullary  body  {corpus  medullare,  Figs.  104 
and  107). 

Function. — The  cerebellum  is  first  of  all  a  correlation  center  for 
the  muscle-  and  static-senses;  and,  second,  a  general  subcerebral 
correlation  center  for  all  forms  of  afferent  impulses.  In  response 
to  these  impulses  it  originates  impulses  which  coordinate 
muscles  and  maintain  equilibrium.  Coordination  is  the  one  well- 
established  function.  The  cerebellum  also  acts  as  a  relay  in 
the  indirect  afferent  and  efferent  paths.  Moreover,  physiolo- 
gists claim  that  it  constitutes  an  augmenter -center,  elevating 
muscle-tone,  increasing  the  power  of  muscular  contraction  and 
accelerating  the  rate  of  motor  discharges  so  as  to  obtain  steady, 
tonic  contraction. 

Divisions. — The  cerebellum  is  made  up  of  two  lateral  parts, 
the  hemispheres,  and  a  central  part,  uniting  the  hemispheres  to- 
gether, called  the  vermis  cerebelli,  or  worm  (Figs.  10 1,  102,  and 
106) .  In  the  early  embryo  the  cerebellum  is  a  transverse 
ridge  in  the  roof  of  the  fourth  ventricle,  partially  divided  for 
a  time  by  a  median  groove  on  its  ventricular  surface;  and  it 
remains  undifferentiated  into  medial  and  lateral  parts  in  many 
lower  animals  (Edinger). 

The  cerebellar  hemispheres  {hemispheria  cerebelli)  measure 
5  cm.  (2  inches)  from  before  backward  and  about  the  same  in 
thickness,  near  the  anterior  end  of  the  vermis;  but  they  taper 
rapidly  toward  the  lateral  borders  (Figs.  loi  and  102).  They 
present  a  sharp  anterior  angle  and  a  rounded  lateral  angle. 
The  hemispheres  are  joined  together  by  the  worm,  or  vermis, 
which  forms  the  central  and  most  elevated  part  of  the 
cerebellum. 

The  vermis  cerebelli,  or  worm,  is  a  small  elongated  lobe, 
shorter  and  much  thinner  than  the  hemisphere  (Figs.  loi  and  106) . 
In  animals  lower  than  mammals  it  is  not  differentiated  from  the 
hemispheres  and  appears  to  be  the  only  part  of  the  cerebellum 


264 


THE   RHOMBENCEPHALON 


present,  being  very  large  in  birds  and  swimming  reptiles  (Edin- 
ger) .  Its  transverse  ridges  give  it  a  worm-like  appearance.  It 
unites  the  upper  half  of  the  medial  aspect  of  the  two  hemi- 
spheres, their  lower  halves  being  separated  by  an  antero-pos- 
terior  groove,  called  the  valley  or  vallecula  cerebelli.  The  upper 
surface  of  the  vermis  is  called  the  superior  worm,  or  vermis 


Fig.  ioi. — Dorsal  view  of  inter-brain,   mid-brain  and  cerebellum.     Superior 
surface  of  cerebellum.     (Original.) 

a.  Pineal  body.  b.  CoUiculus  superior  of  corp.  quad.  c.  Lateral  sulcus,  d.  Colliculus 
inferior  of  corp.  quad.  e.  Culmen  monticuli.  f.  Pars  posterior  of  quadrangular  lobule. 
g.  Superior  sernilunar  lobule,  h.  Anterior  tubercle  of  thalamus,  i.  Stria  medullaris 
thalami.  j.  Trigonum  habenulae.  k.  Mid-brain.  1.  Inferior  horn  of  lateral  ventricle. 
m.  Pars  anterior  of  quadrangular  lobule,  n.  Predeclivil  sulcus,  o.  Post-declivil  sulcus. 
p.  Declive  monticuli.  q.  Folium  vermis,  r.  Posterior  cerebellar  notch,  s.  Horizontal 
sulcus. 


superior;  and  the  lower  surface,  the  inferior  worm,  or  vermis 
inferior.  The  superior  and  inferior  surfaces  are  separated  from 
one  another  at  the  posterior  end  of  the  worm  by  the  great  hori- 
zontal sulcus;  anteriorly,  the  medullary  body  of  the  cerebellum 
separates  them.  At  either  end  of  the  worm  is  a  notch  bounded 
by  the  vermis  and  the  hemispheres,  the  anterior  and  posterior 
cerebellar  notches. 


CORPUS  MEDIJLLARE   CEREBELLI  265 

The  posterior  cerebellar  notch,  incisura  ceredeUi  posterior 
(Fig.  loi),  bounded  by  the  posterior  end  of  the  worm  and  the 
postero-medial  border  of  the  hemispheres,  is  occupied  by  the 
falx  cerebelli.  A  prolongation  of  the  medullary  body  of  the 
cerebellum  fills  up  the  incisura  cerebelli  anterior,  or  anterior 
cerebellar  notch,  which  is  situated  between  the  anterior 
angles  of  the  hemispheres,  in  front  of  the  vermis  cerebelli. 

The  medullary  body  {corpus  medullare)  which  is  the  white 
center  of  the  cerebellum  splits  in  its  median  part  into  two 
lamince;  a  superior,  which  forms  the  superior  medullary  velum 
and  three  pairs  of  connecting  bands  (peduncles),  and  an  infe- 
rior, which  is  the  inferior  medullary  velum  (Figs.  104  and  106). 
Separating  at  an  acute  angle,  the  two  laminae  form  the  tent  of  the 
fourth  ventricle. 

The  inferior  medullary  velum  {velum  medullare  inferius,  Figs. 
104  and  122)  is  the  inferior  lamina  of  the  medullary  body.  It 
is  a  short  plate  of  white  matter,  not  more  than  6  mm.  (3^  inch) 
long  and  is  separated  from  the  superior  lamina  by  the  angle 
called  the  fastigium.  It  ends  in  a  concave  border  from  which  a 
sheet  of  epithelium  continues  down  over  the  fourth  ventricle; 
and  together  they  form  the  inferior  half  of  the  roof  of  that  cavity. 
Laterally,  the  inferior  velum  extends  to  the  flocculus  of  the 
hemisphere.  Of  the  worm  it  covers  the  nodulus,  antero-supe- 
riorly.  It  bounds,  dorsally,  the  lateral  recesses  of  the  fourth 
ventricle. 

The  superior  lamina  of  the  medullary  body  joins  the  cere- 
bellum immediately  to  the  pons.  The  superior  lamina  is  made 
up  of  three  pairs  of  connecting  bands  (cerebellar  peduncles) 
and  the  superior  medullary  velum.  It  constitutes  all  the  pro- 
longations of  the  corpus  medullare  of  the  cerebellum,  except 
the  inferior  velum  (Fig.  122). 

The  brachia  conjunctiva  (superior  peduncles.  Figs.  103  and 
122)  converge  as  they  pass  forward  and  upward  to  the  inferior 

In  the  BNA  the  cerebellar  vela  are  called  "velum  medullare  anterius"  and 
"v.  m.  posterius;"  but  there  is  no  more  reason  for  these  embryological  terms 
in  this  place  than  there  is  elsewhere  throughout  the  central  nervous  system, 
and  I  have  used  "superius"  and  "inferius"  which  properly  indicate  their 
positions  in  adult  anatomy. 


266  THE   RHOMBENCEPHALON 

quadrigeminal  colliculi,  where  they  disappear.  They  are 
joined  to  one  another  by*  a  thin  plate  of  white  matter,  the  supe- 
rior medullary  velum  {velum  medullare  superius).  With  the 
velum  they  form  the  roof  and  lateral  boundaries  of  the  superior 
half  of  the  fourth  ventricle.  They  gradually  bury  themselves  in 
the  pons  as  they  proceed  upward  toward  the  corpora  quadri- 
gemina.  Beneath  the  corpora  quadrigemina  and  the  cerebral 
aqueduct,  the  brachia  conjunctiva  cerebelli  decussate,  and  pass 
into  the  hypothalamic  region  of  the  opposite  side.     They  end 


o  P  q  r 

Fig.  I02. — Anterior  aspect  of  cerebellum.  {Original.) 
a.  Horizontal  sulcus,  b.  Flocculus,  c.  Tonsil,  d.  Superior  medullary  velum,  e.  Lob- 
ulus  centralis,  f.  Culmen  monticuli.  g.  Inferior  medullary  velum,  h.  Brachium  con- 
junctivum.  i.  Restiform  body.  j.  Brachium  pontis.  k.  Peduncle  of  flocculus.  1.  Divi- 
sion in  biventral  lobule,  m.  Lobulus  gracilis,  n.  Lobulus  biventer.  o.  Prepyramidal 
sulcus,     p.   Nodule,     q.  Uvula,     r.  Depression  in  tonsil,     s.  Post-nodular  sulcus. 

chiefly  in  the  red  nuclei,  which  they  embrace  medially.  Near 
the  corpora  quadrigemina  each  brachium  conjunctivum  is 
obliquely  crossed  by  the  lateral  fillet  in  its  course  to  the  inferior 
quadrigeminal  colliculus. 

The  superior  medullary  velum  {valve  of  Vieussens,  Figs.  104, 
106,  and  122),  is  a  trapezoidal  sheet  of  white  substance,  wider 
where  it  fuses  with  the  corpus  medullare  of  the  cerebellum  than 
at  the  mesencephalic  end.  It  forms  the  floor  of  the  groove  be- 
tween the  brachia  conjunctiva  cerebelli  and  the  superior  half  of 
the  roof  of  the  fourth  ventricle.     Its  lateral  borders  fuse  with 


RESTIFORM  BODIES 


267 


and  unite  the  brachia  conjunctiva,  hence  their  name.  In  the 
median  line  its  posterior  surface  presents  a  slight  ridge,  the 
jranulum  veli,  from  either  side  of  which  emerges  the  trochlear 
nerve. 

The  corpora  restiformia  (inferior  peduncles  of  the  cerebellum) 
enter  into  the  cerebellum  between  the  brachium  conjunctivum 
and  the  brachium  pontis  (Figs.  103  and  107).  They  first  run 
obliquely  upward  and  lateralward  in  the  medulla  oblongata, 
where  they  help  to  form  the  floor  and  lateral  boundary  of  the 


Fig.  103. — Dissection  of  rhombencephalon  to  show  brachium  conjunctivum, 
brachium  pontis  and  corpus  restiforme.  {Gordinier,  Sappey  after  Hirschfeld 
and  Leveillc.) 

On  left  side  the  cerebellar  brachia  and  restiform  body  have  been  cut  short;  the  right 
hemisphere  is  cut  obliquely  to  show  connection  with  brachium  conjunctivum  and  corpus 
restiforme.  i.  Median  groove  of  fourth  ventricle.  2.  Medullary  striae.  3.  Restiform 
body.  4.  Clava  in  funiculus  gracilis.  5,5.  Brachium  conjunctivum.  6.  Lateral  fillet. 
7,7:  Lateral  sulcus  of  mid-brain.     8.  Corpora  quadrigemina. 

fourth  ventricle ;  entering  the  pons,  they  bend  sharply  backward 
into  the  cerebellum;  and,  running  lateral  to  the  brachium  con- 
junctivum, proceed  to  the  cortex. 

The  brachia  pontis  (middle  peduncles)  join  the  cerebellum  to 
the  lateral  borders  of  the  pons  (Figs.  103,  in  and  122).  They 
are  continuous  with  the  transverse  fibers  in  the  basilar  part  of 
the  pons.  The  brachia  pontis  in  the  anterior  cerebellar  notch 
are  placed  lateral  to  the  brachia  conjunctiva  and  the  restiform 
bodies. 


268 


THE  RHOMBENCEPHALON 


Horizontal  Sulcus  of  Cerebellum  (Figs.  loi,  104  and  106). 
— ^The  cerebellum  has  one  great  sulcus  which  divides  it  into  upper 
and  lower  surface.  The  sulcus  horizontalis  cerebelli  is  irregu- 
larly circular  in  shape;  anteriorly  its  lips  are  separated  by  the 
prolongation  of  the  medullary  body  from  which  the  sulcus  runs 
backward,  dividing  the  border  of  each  hemisphere  and  the 
posterior  end  of  the  worm.     Rarely  the  two  halves  are  not  con- 


]\  Fig.  104. — Median  section  of  cerebellum,  pons  and  medulla.      (Original.) 

a.  Predeclivil  sulcus,  b.  Arbor  vitae.  c.  Declive  monticuli.  d.  Post-declivil  sulcus,  e. 
Folium  vermis,  f.  Horizontal  sulcus,  g.  Tuber  vermis,  h.  Post-pyramidal  sulcus,  i. 
Pyramid,  j.  Prepyramidal  sulcus,  k.  Uvula.  1.  Culmen  monticuli.  m.  Post-central 
sulcus,  n.  Central  lobule,  o.  Inferior  coUiculus  of  corp.  quad.  p.  Cerebral  aqueduct. 
q.  Precentral  sulcus,  r.  Superior  medullary  velum,  s.  Lingula.  t.  Medial  longitudinal 
bundle,     u.  Fastigium.     v.  Inferior  medullary  velum,     w.  Nodule,    x.  Post-nodular  sulcus. 


tinuous  through  the  posterior  extremity  of  the  worm.  In  the 
horizontal  sulcus  the  remaining  important  sulci  of  the  cere- 
bellum terminate.  They  are  nearly  parallel  with  one  another, 
hence  the  cerebellum  is  laminated,  not  convoluted  like  the 
cerebrum.  Though  the  horizontal  sulcus  is  an  important  land- 
mark in  the  adult  cerebellum,  it  does  not  form  a  primary  em- 
bryonic division  of  the  cerebellum  but  appears  late  in  foetal  life 
(Cunningham). 


SUPERIOR   SULCI   OF   CEREBELLUM  269 

SUPERIOR  SURFACE  OF  THE  CEREBELLUM 

The  superior  surface  of  the  cerebellum  {fades  cerehelli  su- 
perior) is  bounded  by  the  horizontal  sulcus  and  the  superior 
lamina  of  the  medullary  body  (Figs.  loi  and  104).  The  posterior 
and  larger  part  of  this  surface  is  covered  by  the  tentorium 
cerebelli,  the  tentorial  area;  the  small  incisural  area  bounds  the 
anterior  cerebellar  notch.  The  superior  surface  is  divided  into 
five  continuous  lobes  by  four  crescentic  sulci  called  inter- 
lobular sulci. 

Sulci  of  Upper  Surface. — The  interlobular  sulci  {sulci  inter- 
lohulares)  divide  the  worm  and  both  hemispheres  into  lobules; 
and  each  lobe  is  composed  of  a  central  and  two  lateral  lobules. 
These  sulci  are  best  seen  in  a  median  section  of  the  vermis  and 
are  named  in  accordance  with  their  relations  to  the  lobules 
in  the  worm,  viz. : 

1.  The  precentral  sulcus  {s.  prcscentralis) ,  which  is  located 
in  the  anterior  cerebellar  notch  just  above  the  superior  velum 
(Fig.  104)'.  It  is  between  the  lingula  and  lobulus  centralis,  in 
the  worm;  between  the  vinculum  and  ala,  in  the  hemisphere. 
It  terminates  in  the  horizontal  sulcus.  When  the  vinculum  is 
wanting  the  precentral  sulcus  is  present  only  in  the  vermis. 

2.  The  post-central  sulcus  {s.  post-centralis) ,  in  the  worm 
separates  the  lobulus  centralis  from  the  culmen;  and  in  the 
hemisphere  the  ala  from  the  anterior  part  of  the  quadrangular 
lobule  (Figs.  102  and  104).  The  sulcus  is  situated  at  the  upper 
border  of  the  anterior  cerebellar  notch  and  runs  just  under  the 
anterior  border  of  the  tentorial  surface  of  the  cerebellar  hemi- 
sphere. Both  central  sulci  terminate  on  the  dorsum  of  the  supe- 
rior medullary  lamina  in  the  horizontal  sulcus. 

3.  Predeclivil  Sulcus  {S.  prcedeclivis ,  s.  primarius)  (Figs. 
10 1  and  104) . — Behind  the  culmen  and  anterior  part  of  the  quad- 
rangular lobule,  13  mm.  from  the  anterior  border  of  the  ten- 
torial surface,  there  is  the  predeclivil  sulcus.  It  bounds  the 
declive  and  posterior  part  of  the  quadrangular  lobule  in  front. 
It  ends  at  the  junction  of  the  anterior  and  middle  thirds  of  the 
antero-lateral  border  of  the  hemisphere  in  the  horizontal  sulcus. 


270 


THE   RHOMBENCEPHALON 


Embryologically  it  is  second  to  appear;  it  is  the  deepest  sulcus 
of  the  cerebellum,  hence  the  name,  sulcus  primarius,  given  it 


Fig.  105. — Median  section  of  cerebellar  vermis,  showing  arbor  vitae,  the 
lobules  and  sulci.  The  fastigium  of  the  fourth  ventricle  lies  at  the  base  of  the 
arbor  vitae. 

4th  V.  Fourth  ventricle,  a.  Lingula.  b.  Precentral  sul.  c.  Central  lobule,  d.. 
Post-central  sul.  e.  Culmen.  f.  Predeclivil  sul.  g.  Declive.  h.  Post-declivil  sul.  i. 
Folium  vermis,  j.  Horizontal  sul.  k.  Tuber  vermis.  1.  Post-pyramidal  sul.  m.  Pyra- 
mid,    n.  Prepyramidal  sul.     o.  Uvula,     p.  Post-nodular  sul.     q.  Nodule. 

by  Kuithan.     Its  development  begins  near  the  end  of  the  third 
month  in  utero  (Cunningham). 


SUPERIOR  LOBES  OF  CEREBELLUM 


271 


4.  The  post-declivil  sulcus  {s.  post-declivis)  (Figs.  10 1  and  104) 
is  located  in  the  posterior  cerebellar  notch,  from  which  it 
curves  outward  and  forward  in  the  superior  surface  of  the  hemi- 
spheres. It  separates  the  declivil  lobe  from  the  folium  vermis, 
in  the  worm  and  from  the  superior  semilunar  lobules  in  the 
hemispheres.  It  ends  in  the  horizontal  sulcus  at  the  junction 
of  the  posterior  and  middle  thirds  of  the  antero-lateral  border. 
Being  behind  the  crescentic  gyri  of  the  quadrangular  lobule, 
this  sulcus  may  be  called  the  sulcus  post-1  unatus.  It  appears  a 
month  later  than  the  predeclivil  sulcus. 

Sulci  and  lobules  of  the  upper  surface  of  the  cerebellum  from 
before  backward: 


Hemisphere 

Vinculum 

Ala 

Lobulus  quadrangularis, 
pars  anterior 

Lobulus  quadrangularis, 
pars  posterior 

Semilunaris  superior 


Worm 

Lingula 
Precentral  sulcus 
Lobulus  centralis 
Post-central  sulcus 
Culmen  monticuli 

Predeclivil  sulcus 
Declive  monticuli 

Post-declivil  sulcus 
Folium  vermis 
Horizontal  sulcus 


Hemisphere 

Vinculum 

Ala 

Lobulus  quadrangularis,  pars 
anterior 

Lobulus  quadrangularis,  pars 
posterior 

Semilunaris  superior 


Lobes  of  Superior  Surface  (Figs.  loi,  102  and  104). — The  lobes 
of  the  superior  surface  of  the  cerebellum  should  be  studied  first 
in  a  median  section,  where  the  branches  of  the  medullary  body 
{lamince  medullares)  will  guide  the  student  and  where  the  sulci 
are  most  easily  identified.  These  lobes  include  the  divisions 
of  the  worm  and  of  the  hemispheres,  and  are  five  in  number. 

Lingula  and  Vincula,  Lobus  Lingulae.— The  lingula  is  a 
very  small  lobule  of  the  vermis  entirely  concealed  in  the  anterior 
cerebellar  notch  by  the  overhanging  central  lobule.  -It  is  a 
tongue-shaped  group  of  four  or  five  rudimentary  transverse 
gyri.  It  rests  upon  the  superior  medullary  velum,  with  which 
its  white  center  is  continuous.  Laterally,  the  lingula  tapers 
off  and  is  sometimes  represented  in  the  hemisphere  by  a  very 


272  THE   RHOMBENCEPHALON 

thin  gyrus  called  the  vinculum  lingulae.  The  vinculum  is  bounded 
by  the  brachium  conjunctivum  cerebelli  in  front,  and  by  the 
precentral  sulcus  behind.  The  precentral  sulcus  separates  the 
lobe  of  the  lingula  from  the  central  lobe. 

Central  Lobule  and  Alae,  Lobus  Centralis  (Figs.  102  and 
104). — The  lobulus  centralis  is  situated  between  the  precentral 
and  post-central  sulci,  in  the  anterior  cerebellar  notch.  It  covers 
the  lingula  and  in  turn  is  overhung  by  the  culmen.  Four  or 
five  small  transverse  gyri  make  it  up.  On  sagittal  section,  it 
is  seen  to  form  a  single  branch  of  the  corpus  medullare  (arbor 
vitae).  The  gyri  of  the  central  lobule,  continuing  along  the 
anterior  cerebellar  notch  into  either  hemisphere,  form  a  triangu- 
lar or  wing-like  lobule,  the  ala  (ala  lobuli  centralis). 

Culmen  and  Anterior  Part  of  Quadrangular  Lobules,  Lobus 
Culminis  (Figs.  loi  and  104). — In  the  culmen  monticuli  the 
surface  of  the  cerebellum  reaches  its  highest  elevation.  It  is 
a  large  lobule  and  occupies  half  of  the  tentorial  surface  of  the 
worm.  It  is  made  up  of  three  or  four  prominent  gyri,  which 
extend  laterally  into  the  hemispheres;  and,  in  each,  forms  the 
anterior  part  of  the  quadrangular  lobule.  The  pars  anterior 
lobuli  quadrangularis  occupies  about  one-third  of  the  tentorial 
surface  of  the  hemisphere.  The  predeclivil  sulcus  separates 
the  culmen  and  the  pars  anterior  of  either  side  (the  lobe  of  the 
culmen)  from  the  declivil  lobe. 

Declive  and  Posterior  Parts  of  Quadrangular  Lobules,  Lobus 
Declivis  (Figs.  loi  and  104). — The  declive  monticuli  forms  the 
posterior  slope,  as  the  culmen  forms  the  summit,  of  the  mon- 
ticulus  cerebelli.  The  declive  has  about  half  the  extent  of  the 
culmen.  Its  gyri  are  continued  into  either  hemisphere,  where 
they  form  a  large  crescentic  lobule,  the  pars  posterior  lobuli 
quadrangularis.  The  increased  size  of  the  lobe  in  the  hemisphere 
is  due  to  the  expansion  of  the  secondary  gyri  found  in  the  worm 
The  anterior  and  posterior  parts  of  the  quadrangular  lobule 
constitute  the  lobulus  quadrangularis  which  forms  the  anterior 
two-thirds  of  the  tentorial  surface  of  the  hemisphere.  The 
declive  and  its  hemispheral  extensions  are  inclosed  between  the 
predeclivil  and  post-declivil  sulci. 


INFERIOR   SURFACE   OF   CEREBELLUM  273 

The  folium  vermis  and  superior  semilunar  lobules,  lobus 
folii  vermis  (Figs.  loi  and  104),  lies  behind  the  post-declivil  and 
above  the  horizontal  sulcus.  The  folium  vermis  is  the  terminal 
lobule  in  the  superior  worm,  and  occupies  the  posterior  cere- 
bellar notch.  It  appears  near  birth  in  the  bottom  of  a  trans- 
verse groove  common  to  the  post-declivil  and  horizontal  sulci 
(Cunningham).  Rarely  it  is  absent.  It  contains  a  single 
medullary  lamina  beset  with  rudimentary  gyri,  which  are 
largely  developed  in  the  hemispheres.  The  superior  semilunar 
lobule  is,  therefore,  very  large  in  comparison  with  the  folium 
vermis.  It  expands  lateralward  to  the  postero-lateral  border  of 
the  hemisphere,  which  it  forms.  It  comprises  the  posterior 
third  of  the  hemisphere's  tentorial  surface,  and  forms  one  of 
the  remarkable  features  of  the  human  cerebellum. 

INFERIOR  SURFACE  OF  THE  CEREBELLUM 

The  inferior  surface  of  the  cerebellum  (fades  cerehelli  inferior) 
is  prominent  laterally  and  depressed  centrally  (as  the  organ  is 
viewed  inverted),  the  hemispheres  being  separated  by  the  antero- 
posterior groove,  called  the  vallecula  cerehelli  (Figs.  102  and  106). 
The  vallecula  (little  valley)  is  occupied  by  the  inferior  worm  and 
is  bounded  on  either  side  by  a  small  cleft,  between  the  worm  and 
the  overhanging  hemisphere,  called  the  sulcus  valleculce.  The 
inferior  cerebellar  surface  is  limited  by  the  horizontal  sulcus 
and  is  separated  from  the  medulla  by  the  transverse  fissure  of  the 
cerebellum.  It  is  more  complex  than  the  superior  surface;  and 
its  sulci  are  more  sharply  curved  forward  as  they  pass  from  the 
worm  into  the  hemispheres. 

Sulci  of  Lower  Surface  (Fig.  106). — The  interlobular  sulci 
of  this  surface  are  very  deep.  They  are  three  in  number, 
namely: 

I.  The  post-nodular  sulcus  (s.  post-nodularis)  (Figs.  102, 
104  and  106)  is  in  the  anterior  end  of  the  worm  between  the  nodule 
and  uvula.  In  the  hemisphere  it  winds  forward  and  outward 
between  the  inferior  medullary  velum  and  the  tonsil  and  then 
continues  lateralward  between  flocculus  and  biventral  lobule 
18 


274 


THE   RHOMBENCEPHALON 


to  the  horizontal  sulcus.     It  is  the'  first  cerebellar  sulcus  to  be 
developed  (Cunningham). 

2.  The  prepyramidal  sulcus  (s.  prmpyramidalis)  (Figs.  104 
and  106),  situated  between  the  uvula  and  pyramid,  is  very  con- 
cave in  the  hemispheres.  It  curves  outward  and  forward 
around  the  tonsil,  separating  it  from  the  biventral  lobule.  It 
terminates  behind  the  flocculus  in  the  post-nodular  sulcus. 

3.  The  post-pyramidal  sulcus  {s.  post-pyramidalis)  (Figs. 
104  and  106),  between  the  pyramid  and  tuber  vermis,  is  near  the 


Fig.  106. — Inferior  surface  of  cerebellum.  {Original.) 
a.  Pyramid,  b.  Flocculus,  c.  Nodule,  d.  Brachium  pontis.  e.  Restiform  body.  f. 
Superior  medullary  velum,  g.  Brachium  conjunctivum.  h.  Quadrangular  lobule,  i. 
Post-nodular  sulcus,  j.  Uvula,  k.  Tuber  vermis.  1.  Ant.  and  m.  Post.  Slender  lobules. 
n.  Inferior  semilunar  lobule,  o.  Tonsil,  p.  Biventral  lobule,  q.  Horizontal  sulcus,  r. 
Lobulus  gracilis,  s.  Prepyramidal  sulcus,  t.  Post-pyramidal  sulcus,  u.  Post,  cerebellar 
notch.    V.  Sulcus  valleculae. 


posterior  end  of  the  worm.  It  forms  an  oblique  groove  in  either 
sulcus  valleculae,  from  which  three  concentric  sulci  extend  into 
the  hemisphere.  The  anterior  of  the  three  (the  pregracile), 
usually  considered  the  post-pyramidal  sulcus  in  the  hemisphere, 
separates  the  biventral  lobule  from  the  slender  lobule  (1.  gracilis) ; 
the  remaining  two  (mid-gracile  and  post-gracile)  subdivide  the 
slender  lobule  into  anterior  and  posterior  slender,  and  separate 
the  lobulus  gracilis  from  the  inferior  semilunar  lobule.  The 
last  is  bounded  behind  by  the  horizontal  sulcus. 


INFERIOR   LOBES    OF   CEREBELLUM  275 

Sulci  and  lobules  of  the  lower  surface  of  the  cerebellum,  from 
before  backward: 

Hemisphere  Worm  Hemisphere 

Flocculus  Nodule  Flocculus 

Post-nodular  sulcus 
Tonsil  Uvula  Tonsil 

Prepyramidal  sulcus 
Biventral  lobule  Pyramid  Biventral  lobule 

Post-pyramidal  sulcus 
Slender  lobule  and  infe-     Tuber  vermis  Slender    lobule    and    inferior 

rior  semilunar  lobule        Horizontal  sulcus  semilunar  lobule 

Lobes  of  Lower  Surface. — They  are  not  continuous  from  the 
worm  to  the  hemisphere  as  on  the  upper  surface  (Figs.  loi  and 
106).  Excepting  in  the  posterior  lobe,  only  a  small  ridge  be- 
neath the  sulcus  valleculas  joins  the  central  and  lateral  lobules 
together.  The  inferior  lobes  are  four  in  number.  Each  is 
composed  of  a  central  and  two  lateral  lobules  as  on  the  upper 
surface.     The  lobule  in  the  worm  gives  its  name  to  the  lobe. 

Nodule  and  Flocculi,LobusNoduli  (Figs.  104  and  106). — The 
nodule  (nodulus  vermis)  is  a  small  lobule  at  the  anterior  end  of 
the  inferior  worm.  It  is  composed  of  three  or  four  gyri,  which 
project  from  the  middle  of  the  dorsal  surface  of  the  inferior  med- 
ullary velum.  It  comprises  a  single  branch  of  the  arbor  vitae. 
Though  larger  it  is  the  counterpart  of  the  Hngula  on  the  superior 
velum.  It  is  bounded  by  the  sulcus  valleculas  on  either  side. 
The  inferior  medullary  velum  extends  laterally  from  the  nodule 
and  in  part  blends  with  the  brachium  pontis  of  the  cerebellum. 
In  front  of  the  tonsil  a  layer  of  gray  matter  {pedunculus  fiocculi) 
appears  on  the  velum.  That  gray  matter  enlarges  more 
laterally  to  a  small  tufted  mass,  called  the  flocculus,  in  which 
the  velum  ends.  Embryologically,  the  flocculus  is  the  oldest 
lobule  of  the  human  cerebellum,  as  is  the  floccular  sulcus  (post- 
nodular  sulcus)  which  bounds  it,  the  first  one  formed.  The 
flocculus  is  very  small  and  rudimentary  in  man.  It  is  divided 
into  an  anterior  and  a  posterior  part,  the  latter  being  called 
the  secondary  flocculus.  The  flocculus  is  separated  from  the 
tonsil  and  the  biventral  lobule  by  the  post-nodular  sulcus.     The 


276  THE   EHOMBENCEPHALON 

whole  line  of  structures,  namely,  the  nodule,  velum,  peduncle 
and  flocculus,  form  the  lobe  of  the  nodule. 

Uvula  and  Tonsils,  Lobus  Uvulae  (Figs.  104  and  106). — The 
uvula  (uvula  vermis)  comprises  a  considerable  part  of  the  vermis 
inferior  behind  the  nodule.  It  broadens  backward  and  is  widest 
next  the  pyramid.  Bounded  on  either  side  by  the  sulcus  val- 
leculae,  it  projects  into  the  valley  like  the  uvula  into  the  isthmus 
of  the  fauces.  It  comprises  one  large  branch  of  the  arbor  vitae 
which  bifurcates  near  its  origin  into  two  laminae  and  presents 
at  the  surface  six  or  eight  small  gyri.  A  slight  ridge,  the  fur- 
rowed band,  joins  it  to  the  tonsil  (tonsilla  cerebelli)  in  the  hemi- 
sphere. From  the  furrowed  band  the  tonsil  expands  downward 
and  backward,  forming  a  lobule  of  nearly  a  dozen  sagittal  gyri. 
The  tonsil  overhangs  the  side  of  the  uvula  and  conceals  the  fur- 
rowed band,  medially;  and,  behind,  it  conceals  the  connecting 
ridge  between  the  pyramid  and  biventral  lobule.  Its  large  size 
makes  it  a  prominent  feature  of  the  human  cerebellum.  The 
fossa  containing  the  tonsil  is  the  bird's  nest  (nidus  avis).  Be- 
hind the  uvular  lobe,  composed  of  the  above  three  lobules,  is  the 
prepyramidal  sulcus. 

Pyramid  and  Biventral  Lobules,  Lobus  Pjaramidis  (Figs.  104 
and  106). — As  seen  from  the  surface,  three  or  four  distinct  gyri 
make  up  the  pyramid  (pyramis  vermis);  in  reality,  it  covers 
one  strong  lamina  of  the  arbor  vitae,  which  divides  into  two  near 
the  surface.  It  forms  the  most  prominent  lobule  of  the 
inferior  worm.  A  low  connecting  ridge  joins  the  pyramid  to  the 
biventral  lobule  in  the  hemisphere.  The  biventral  lobule  (lobu- 
lus  biventer)  is  triangular  in  outline.  Its  base  looks  toward  the 
flocculus  and  is  bounded  by  the  post-nodular  and  the  horizontal 
sulcus;  its  apex  is  continuous  with  the  connecting  ridge  joining 
it  to  the  pyramid.  The  gyri  composing  it  radiate  from  the  apex 
toward  the  base,  and  are  divided  into  two  groups  by  a  very  deep 
intralobular  sulcus.  Its  lateral  extension  is  a  little  beyond  the 
flocculus.  The  post-pyramidal  sulcus  bounds  it  postero-later- 
ally,  and  separates  it  from  the  slender  lobule. 

Tuber  Vermis,  Slender  and  Inferior  Semilunar  Lobules, 
Lobus  Tuberis  (Figs.  104  and  106). — The  tuber  vermis  forms  the 


SLENDER   AISTD   INFERIOR   SEMILUNAR   LOBULES 


277 


posterior  end  of  the  inferior  worm.  It  resembles  the  lobules  of 
the  vermis  superior,  because  some  of  its  half  dozen  tertiary  gyri 
are  continued  into  the  hemispheres,  the  sulcus  valleculae  not 
cutting  them  off.  A  bifurcated  lamina  of  the  arbor  vitae  enters 
into  the  tuber.  The  horizontal  sulcus  separates  it  from  the 
folium  vermis  of  the  superior  worm.  The  slender  and  inferior 
semilunar  lobules  comprise  the  posterior  two-thirds  of  the  in- 
ferior surface  of  each  hemisphere,  extending  from  the  biventral 


Fig.  107. — Sagittal  section  of  cerebellum,  cutting  nucleus  dentatus.     {Original.) 

a.  Sup.  semilunar  lobule,  b.  Corpus  meduUare.  c.  Post,  part  quadrangular  lobule,  d. 
Nucleus  dentatus.  e.  Ant.  part  of  quadrangular  lobule,  f.  Interior  of  dentate  nuc.  g. 
Central  sulci,  h.  Brachium  pontis.  i.  Restiform  body.  j.  Inf.  semilunar  and  slendef 
lobules,     k.  Hilus  of  nuc.  dent.     1.  Biventral  lobule. 


lobule  to  the  posterolateral  border.  Twelve  to  fifteen  gyri 
compose  the  lobules.  The  gyri  are  divided  into  three  groups 
by  the  midgracile  and  post-gracile  sulci;  the  anterior  and  middle 
groups  are  named  the  anterior  slender  and  posterior  slender 
lobules,  they  constitute  the  lobulus  gracilis.  The  posterior  is 
the  inferior  semilunar  lobule.  The  inferior  semilunar  lobule, 
only,  is  continuous  with  the  gyri  of  the  vermis.  The  great 
size  of  the  inferior  and  superior  semilunar  lobules  is  the  most 
characteristic  feature  of  the  human  cerebellum. 


278  THE    RHOMBENCEPHALON 

The  gray  matter  of  the  cerebellum  is  composed  of  cortex 
which  covers  the  cerebellar  laminae  and  of  nuclei  imbedded  in 
the  medullary  body  (Figs.  108  and  109). 

I.  CORTICAL  GRAY  MATTER 

The  cerebellar  cortex  is  inexcitable  (Horsley  and  Clarke). 
It  originates  no  fibers  that  pass  out  of  the  cerebellum,  only 
cortico-nuclear  fibers;  but,  with  very  few  exceptions,  it  receives 
all  fibers  that  enter  the  cerebellum.  The  cerebellar  cortex  is  a 
great  receptive  organ  which  correlates  afferent  impulses.  The 
impulse-complex,  produced  by  such  correlations,  passes  through 
the  cortico-nuclear  fibers  to  the  cerebellar  nuclei,  and  leaves  the 
cerebellum  through  the  nucleo-fugal,  or  cerebello-tegmental 
fibers;  ultimately  it  arrives  in  motor  nuclei  and  regulates  their 
discharges  so  as  to  secure  coordinated  movement  (Brain,  Vols.  28, 
29,  31,  etc.). 

The  cortex  of  the  cerebellum  {substantia  corticalis  cerebelli) 
is  made  up  of  two  thick  layers  visible  to  the  naked  eye,  viz.,  (i) 
a  superficial  layer,  and  (2)  a  deep,  granular  layer.  At  the  junc- 
tion of  these  two  layers  is  a  single  row  of  large  pitcher-shaped 
cell-bodies,  which  are  characteristic  of  the  cerebellar  cortex 
and  are  almost  visible  to  the  unaided  eye.  They  are  the  bodies 
of  Purk.inje^s  cells,  and  are  considered  in  the  deep  part  of  the 
first  macroscopic  layer,  where  they  form  the  stratum  gangliosum. 
Under  the  microscope  three  layers  are  easily  seen,  viz.,  (i)  the 
gray  layer  (stratum  cinereum);  (2)  the  ganglion  cell  layer 
(stratum  gangliosum);  and  (3)  the  granular  layer  (stratum 
granulosum) . 

I.  Superficial  Layer  (Figs.  108  and  109). — Thickest  on  the 
laminae  and  thinnest  beneath  the  sulci,  this  layer  contains 
small  and  large  stellate  cell-bodies  with  their  processes,  which 
constitute  the  stratum  cinereum  proper;  and  the  large  Purkinje 
cell-bodies  with  their  dendrites  and  recurrent  collaterals,  to- 
gether with  many  corticipetal  fibers.  The  Purkinje  cells  form 
the  stratum  gangliosum. 

Cells. — The  bodies  of  Purkinje's  cells  (Figs.  108  and  109) 
are  located  near  the  deep  surface  of  the  superficial  layer  in  the 


CEREBELLAR   CORTEX  279 

stratum  gangliosum.  They  measure  from  loo/x  to  135^  in  their 
longest  axis,  6o/i  in  diameter.  Each  has  one  axone  which,  after 
piercing  the  deep  layer,  becomes  a  fiber  of  the  medullary  body. 
It  medullates  very  close  to  the  cell-body  and  gives  off,  in  the 
deep  layer,  several  recurrent  collaterals,  which  form  contact  rela- 
tions with  other  cells  in  both  layers.  From^the  outer  end  of 
each  cell-body  antler-like  processes,  the  dendrites,  are  given  off; 
they  ramify  toward  the  surface  in  a  wide  plane  at  right  angles 
to  the  free  border  of  the  gyrus.  The  edge  of  the  plane  only  is 
seen  in  a  longitudinal  section  of  the  gyrus  and  the  arborization 
is  very  narrow  and  tall.  The  stellate  cell-bodies,  an  outer  and 
inner  layer,  together  form  the  stratum  cinereum.  They  measure 
io-20/i  and  increase  in  size  toward  the  Purkinje  cells.  They 
have  rich  dendritic  processes  and  one  axis-cylinder  each.  Their 
processes  ramify  throughout  the  stratum  cinereum  and  stratum 
gangliosum.  The  inner  layer  of  the  stratum  cinereum  contains 
the  larger  cells;  they  are  called  the  '' basket  cells."  Their  axis- 
cylinder  processes  run  parallel  with  the  surface  and  at  right 
angles  to  the  border  of  the  gyrus;  they  give  off  vertical  branches, 
which  descend  to  Purkinje's  corpuscles  and  inclose  them  in  a 
basket  work  of  filaments.  In  the  outer  layer  of  the  stratimi 
cinereum  the  stellate  cell-bodies  are  smaller  than  in  the  inner 
layer.  They  branch  freely  and  terminate  in  end- tufts  in  contact 
with  other  stellate  cells. 

The  fibers  of  the  superficial  layer  (Figs.  io8  and  109)  have 
three  sources:  {a)  The  processes  of  neurones  within  the  layer, 
which  include  the  dendrites  and  axones  of  the  stellate  cells  and 
the  dendritic  planes  and  recurrent  collaterals  of  Purkinje's  cells. 
{h)  The  processes  of  cell-bodies  in  the  deep  layer,  whose  T- 
branched  axones  pierce  the  dendritic  planes  of  Purkinje  in  the 
first  layer;  and,  the  processes  of  the  large  granules  whose  den- 
drites ramify  toward  the  surface,  {c)  The  fibers  of  the  medul- 
lary projection  rise  or  end  largely  in  the  cellular  layer.  The 
axones  of  Purkinje's  neurones  compose  all  of  the  corticifugal 
fibers.  They  end  in  the  cerebellar  nuclei  of  the  cat,  dog  and 
monkey  (Clark  and  Horsley)  also,  in  the  rabbit  (Van  Ge- 
huchten)  and  probably  have  these  endings  in  the  human  brain. 


28o 


THE   RHOMBENCEPHALON 


The  corticipetal  fibers,  which  rise  either  in  other  parts  of  the 
brain  or  in  the  spinal  cord  and  ganglia,  terminate  in  varicose 
fibrils  chiefly  in  the  superficial  layer.  These  fibrils  entwine 
about  the  ^'primary  and  secondary  stems  of  the  Purkinje 
dendrites"  (Cunningham). 

2.  The  deep,  granular  layer  {stratum  granulosum,  Figs.  io8 
and  109)  is  of  uniform  thickness.  It  blends  centrally  with  the 
medullary  projection.     It  contains  a  few  superficial  granules 


Fig.  108. — Section  of  cerebellar  gyrus  made  parallel  with  its  free  border. 
Diagrammatic.     (After  Kolliker  from  Cunningham.) 

Or  R.  Small  granules  with  claw-shaped  dendrites  and  long  axones  that  run  out  into  the 
gray  layer  and  divide  T-like.  N.  Axones  of  small  granule.  P.  Pvirkinje  cells  seen  in 
profile,  showing  border  of  dendritic  planes  in  gray  layer. 

which  are  large  in  size  (60-80 /i)  and  many  small  granules  in 
which  the  nucleus  occupies  nearly  the  whole  cell-body. 

Cells  of  the  Granular  Layer. — ^The  granules  are  small,  round, 
or  stellate  cell-bodies  (7-1  o/x),  largest  near  Purkinje's  cells, 
closely  packed  externally,  but  scattered  among  the  projection 
fibers  centrally.  Each  small  granule  has  three  to  five  short 
dendrites,  which  soon  break  up  into  claw-like  tufts  in  contact 
with  adjacent  granules,  and  one  long  axone.     The  axone  runs 


GRANULE    CELLS 


281 


out  into  the  superficial  layer,  branches,  T-like,  and,  piercing 
the  dendritic  planes  of  Purkinje,  gives  off  collaterals  to  them 
until  exhausted  by  multiple  division.  It  runs  parallel  with  edge 
of  the  gyrus.     The  large  granules  (60-80  m)  are  dendraxones. 


Fig.  109. — Section  across  a  cerebellar  gyrus  at  a  right  angle  to  the  free  border. 
Diagrammatic.     {Gordinier  after  Van  Gehuchten.) 

Showing  large  stellate  cells  of  first  layer  with  their  basket-work  endings;  the  cells  of 
Purkinje,  their  dendritic  planes  in  the  gray  layer  and  their  axones  running  through  the 
granular  layer  to  the  medullary  lamina  of  the  gyrus;  two  large  granules  of  Golgi  type    '' 
small  granules  whose  T-branches  run  parallel  with  the  border  of  the  gyrus;  moss-like 
ings  of  Cajal,  etc. 


e;  the 
end- 


the  type  of  Golgi.  The  axones  form  remarkable  arborizations 
toward  the  medullary  projection,  touching  and  associating 
many  granules.  The  dendrites,  branching  freely,  ramify  in 
the  superficial  layer. 


282  THE   RHOMBENCEPHALON 

Fibers  of  the  Granular  Layer  (Figs.  108  and  109). — The  nerve 
fibers  of  the  granular  layer  are  as  follows:  (a)  The  processes  of 
the  granules,  (b)  the  axones  of  Purkinje's  cells  running  down 
into  the  medullary  projection,  together  with  their  recurrent 
collaterals,  and  (c)  corticipetal  fibers,  most  of  which  run  through 
the  granular  layer,  without  branching,  to  end  in  the  first 
layer;  the  remainder  terminate  in  the  deep  layer  in  the  moss- 
like appendages  of  Cajal. 

The  functions  of  the  stellate  cells,  the  ''basket  cells"  and  the 
granule  cells  are  probably  receptive  and  associative;  they  re- 
ceive impulses  through  the  projection  fibers  and  transfer  those 
impulses  to  the  dendrites  or  bodies  of  Purkinje's  cells.  Purk- 
inje's cells  originate  impulses  for  the  coordination  of  muscu- 
lar action,  the  preservation  of  muscle-tone,  and  the  produc- 
tion of  powerful  tonic  contractions.  Lesions  in  the  cerebel- 
lum produce  incoordination,  chorea,  athetosis  and,  rarely, 
convulsions. 

The  neuroglia  of  the  cerebellum  is  similar  to  that  in  the  cere- 
brum. The  short-rayed  cells  are  scattered  throughout  the  gray 
substance,  while  the  long-rayed  are  located  near,  or  within,  the 
white  substance.  In  the  region  of  Purkinje's  cells,  near  the 
surface  of  the  deep  layer,  are  the  bodies  of  the  arborescent  cells, 
whose  processes  form  a  fine  interlacement  about  the  cell- 
bodies  of  Purkinje  and  then  extend  in  parallel  lines  out  to  the 
surface.  They  form  a  neuroglia  felt-work  just  beneath  the  pia 
mater  (lamina  basalis). 

Histogenesis  of  Cerebellar  Cortex  and  Nuclei. — The  dorsal  laminae  and 
roof-plate  of  the  metencephalon,  in  which  the  cerebellum  is  developed, 
very  early  show  a  stratification  into  three  layers.  The  stratification  here  is 
the  same  as  occurs  elsewhere  in  the  neural  tube,  the  layers  being  the  epen- 
dymal,  mantle  and  marginal  layers,  from  within  outward.  The  neurones  of 
the  cerebellum  are  derived  from  two  sources;  i.  The  mantle  layer  of  the 
cerebellum  and  2.  the  rhombic  lip  of  the  medtdla  oblongata.  All  cortical 
neurones,  except  those  of  Purkinje,  are  emigrant  cells  from  the  rhombic 
lip.  The  nuclear  neurones  are  natives  of  the  dorsal  laminae,  intrinsic 
neurones. 

I.  The  intrinsic  neuroblasts  of  the  mantle  layer  throw  out  their  primary 
pseudppods  and  develop  their  axones  in  the  direction  of  the  ventricular 


HISTOGENESIS    OF    CEREBELLUM  283 

cavity.  In  accordance  with  the  relations  they  acquire,  these  neurones  faU 
into  Pwo  classes,  nuclear  and  cortical,  (i)  The  nuclear  neuroblasts  push 
their  axones  (cerebello-tegmental  fibers)  out  into  other  parts  of  the  brain 
and  form  synapses  with  neurones  in  the  thalamus,  mid-brain,  pons  and 
medulla;  their  cell-bodies  receive  the  end-tufts  of  the  cortical  neurones. 
(2)  The  cortical  neuroblasts  of  the  mantle  layer  develop  wholly  within  the 
cerebellum.  As  just  stated,  their  axones  (cortico-nuclear  fibers)  form 
synapses  with  the  dendrites  and  bodies  of  the  nuclear  neurones. 

In  the  development  of  a  neuroblast  the  push  of  "the  cone  of  growth" 
at  the  end  of  the  axone  must  be  equaled  by  the  resistance  offered  to  the 
opposite  side  of  the  neuroblast.  Conditions  being  equal,  the  advance  of 
'*the  cone  of  growth"  and  the  retreat  of  the  cell-body  are  inversely  pro- 
portional to  the  area  of  the  pushing  surfaces.  Because  of  this  simple  fact, 
the  bodies  of  the  nuclear  neurones  tend  to  recede  from  the  ventricle  as  their 
axones  push  toward  it;  but,  being  resisted  by  the  axonic  push  of  the  cor- 
tical neurones,  they  remain  close  to  the  ventricle  and  constitute  the 
dentate,  emboliform,  globose  and  fastigial  nuclei.  The  nuclear  cells  form 
fixed  points  of  resistance  for  the  intrinsic  cortical  neurones;  hence,  as  their 
axones  grow,  their  bodies  are  pushed  out  into  the  marginal  layer,  where 
they  take  up  their  adult  positions  and  develop  into  the  wonderful  cells 
of  Purkinje. 

The  stellate  and  granule  cells  of  the  cerebellar  cortex  are  all  immigrants. 
They  migrate  from  the  sensory  column  of  the  medulla,  located  in  the  lip  of 
the  rhomboid  fossa  (fourth  ventricle).  In  the  latter  part  of  the  second 
month  this  migration  begins;  it  continues  to  flow  steadily  until  the  super- 
ficial part  of  the  marginal  layer  is  crowded  with  cells.  It  appears  to  be  a 
passive  migration,  the  cells  being  carried  into  the  cerebellum  by  the  in- 
growing tracts  from  the  pons  and  spinal  cord.  In  the  marginal  layer  a 
large  number  of  the  immigrant  cells  complete  their  life  histories,  throwing 
out  their  axones  and  dendrites  and  establishing  relations  with  one  another, 
with  the  corticipetal  axones  and  with  the  cells  of  Purkinje;  but  a  consider- 
able number  of  small  neuroblasts,  whose  axones  are  directed  toward  the 
surface,  leave  this  superficial  position.  Their  axones  branch  T-like, 
diverging  parallel  with  the  edge  of  the  gyri;  and,  with  the  growth  of  the 
axones,  the  cell-bodies  gradually  sink  down  between  the  Purkinje  cells  into 
the  mantle  layer.  Such  centripetal  migration  continues  until  a  dense  layer 
of  small  cell-bodies  is  formed  subjacent  to  the  cells  of  Purkinje.  The  cell- 
bodies  possess  so  little  cytoplasm  the  layer  looks  like  a  collection  of  nuclei 
or  granules,  hence,  the  name,  granular  layer.  Each  granule  cell  gives  off 
four  to  eight  dendrites  that  end  in  the  form  of  claw-like  tufts;  they  estab- 
lish synapses  with  one  another,  with  the  large  second  type  cells  of  the 
granular  layer  and  with  some  of  the  corticipetal  fibers. 


284 


THE   RHOMBENCEPHALON 


n.  NUCLEAR  OR  GANGLIONAR  GRAY  MATTER 

The  nuclei  of  the  cerebellum  are  the  nucleus  dentatus, 
nucleus  emboliformis,  nucleus  globosus  and  nucleus  fastigii 
(Figs.  107  and  no).  All  these  nuclei  are  made  up  of  stellate 
cell-bodies,  which  vary  in  size  from  20-80  microns.  They 
form  relay  stations  in  the  paths  going  out  of  the  cerebellum.     They 


Fig.  no. — Horizontal  section  of  cerebellum  cutting  nuclei  and  brachia  con- 
junctiva. {Morris's  Anatomy  after  Toldt.) 
a.  Interpeduncular  fossa,  b.  Cerebral  peduncle,  c.  Raphe  of  medulla  oblongata,  d. 
Medial  longitudinal  fasciculus,  e.  Lateral  lemniscus,  f.  Substantia  ferruginea.  g. 
Superior  medullary  velum,  h.  Lingula  cerebelli.  i.  Nucleus  emboliformis.  j.  Nucleus 
fastigii.  k.  Nucleus  globosus.  1.  Vermis  (superior),  m.  Posterior  cerebellar  notch. 
n.  Pons  (varolii),  o.  Decussation  of  brachium  conjunctivum.  p.  Stratum  nucleare. 
q.  Fossa  rhomboidea  (pars  superior),  r.  Fourth  ventricle,  s.  Brachium  conjunctivum. 
t.  Hilus  of  dentate  nucleus,  u.  Core  of  the  dentate  nucleus,  v.  Dentate  nucleus,  w. 
Capsule  of  dentate  nucleus,  x.  Corpus  meduUare.  y.  Cortical  substance,  z.  Medullary 
lamina. 


originate   all   cerebello-fugal  fibers j    called   cerebello- tegmental 
fasciculi.     In  them  terminate  axones  of  Purkinje^s  cells. 

The  nucleus  dentatus  (corpus  dentatum)  is  a  wavy,  sinuous 
pouch  of  yellowish-brown  gray  matter  imbedded  in  the  medul- 
lary body  of  each  hemisphere.  The  nucleus  dentatus  meas- 
sure  15-20  mm.  in  length  and  7-10  mm.  in  width  (Fig.  107). 
It  is  filled  with  white  fibers,  which  issue  from  its  open  anterior 


SMALL   CELLULAR  NUCLEI  285 

end,  called  the  hilus,  and  form  the  greater  part  of  the  brachium 
conjunctivum  cerebelli.  It  also  receives  many  axones  from 
Purkinje^s  cells  and,  thus,  forms  a  relay  in  the  common  sen- 
sory path,  also  in  the  cerebello-rubro-spinal  coordinating 
path. 

The  small  nuclei  are  visible  to  the  naked  eye  under  favor- 
able conditions  (Fig.  no).  One  of  these,  a  club-shaped  mass, 
the  cork-like  nucleus  emboliformis,  partly  closes  the  hilus  of  the 
dentate  nucleus.  It  measures  15  mm.  in  length,  6  mm.  in 
width  and  3  mm.  in  thickness.  It  is  in  part  continuous  with 
the  dentate  nucleus  and  is  closely  allied  to  it  in  function,  re- 
ceiving cortical  axones  and  contributing  its  own  to  the  brachium 
conjunctivum.  Medial  to  it  is  an  elongated  antero-posterior 
nucleus,  bulbous  in  front,  called  the  nucleus  glohosus.  The 
nucleus  globosusis  intimately  related  to  the  emboliform  nucleus; 
and,  like  it,  is  a  dissociated  part  of  the  nucleus  dentatus.  These 
three  nuclei  probably  represent  the  lateral  cerebellar  nucleus 
found  in  lower  vertebrates  (Edinger).  The  spherical  head 
of  the  nucleus  globosus,  somewhat  flattened  on  either  side, 
lies  just  above  the  tonsil;  it  measures  5  mm.  in  diameter:  its 
slender  tail  extends  backward  about  8  mm.  (Piersol).  The 
third  small  nucleus  of  the  cerebellum  lies  next  the  median 
plane,  in  the  anterior  end  of  the  vermis.  It  is  just  above  the 
fastigium  of  the  fourth  ventricle  and  is  called  the  nucleus  of 
the  highest  point  of  the  roof,  nucleus  fastigii  (Stillingi).  The 
nucleus  fastigii  is  not  found  in  the  lower  vertebrates;  it  first 
appears  in  the  turtle  (Chelone  midas)  and  is  well  developed 
only  in  birds  and  mammals  (Edinger).  In  man  it  is  of  ovoid 
shape,  lo  mm.  long,  circular  in  cross  section  and  5  mm.  in 
diameter.  It  lies  between  the  anterior  and  posterior  com- 
missures of  the  cerebellum,  and  is  joined  to  its  mate  by  the 
fastigial  commissure. 

The  nucleus  fastigii  contains  very  large  stellate  cells,  40-80 
microns  in  diameter;  the  cells  of  the  nuclei  globosus,  emboli- 
formis and  dentatus  are  stellate  in  form,  but  measure  only  20- 
30  microns.  All  nuclear  neurones  of  the  cerebellum  receive 
axones  of  Purkinje's  cells  in  the  cortex.     The  axones  of  the 


286  THE   RHOMBENCEPHALON 

small  cells  pass  chiefly  through  the  brachium  conjunctivum  to 
red  nucleus  and  thalamus,  and,  according  to  Cajal,  give  off 
collaterals  to  the  motor  nuclei  of  mid-brain,  pons  and  medulla. 
These  form  the  superior  group  of  cerehello-tegmental  fibers. 
They  form  a  link  in  a  coordination  path  especially  concerned 
with  locomotion  (Horsley).  The  large  cells  of  the  nucleus 
fastigii  receive,  in  addition  to  the  cortical  axones,  vestibular 
fibers  both  directly  from  the  vestibular  nerve  and  from  the 
vestibular  nuclei.  The  greater  number  decussate  in  the  ver- 
mis before  entering  the  nucleus.  The  axones  of  the  fastigial 
neurones  decussate  in  the  same  situation  and  descend  with 
some  axones  of  the  small-celled  nuclei  to  the  nucleus  of  Deiters 
in  the  medulla  and  to  the  motor  nuclei  of  certain  cranial  nerves 
(V,  VII,  X);  they  form  the  fastigio-bulbar  fasciculus  of  the 
cerebello -tegmental  fibers.  The  nucleus  fastigii  is  a  part  of 
the  vestibular  mechanism  of  equilibrium. 

The  White  Substance  of  the  Cerebelliun  (Figs.  104  and  107). 
— The  corpus  medullare  contains  all  the  white  matter  of  the 
cerebellum.  It  is  a  strong  body  measuring  9  mm.  (J^  in.) 
in  thickness  vertically  in  the  middle  of  the  hemisphere,  but  in 
the  worm  it  is  a  thin  sheet  and  is  very  slender  as  seen  in  a  median 
section.  Its  branches  to  the  cerebellar  gyri  are  called  the 
medullary  lamince  {lamince  medullares).  Viewed  in  a  sagittal 
section  of  the  hemisphere,  the  medullary  laminae  are  short  and 
stubby  branches  of  a  very  thick  trunk;  but  the  tree-like  ap- 
pearance of  the  medullary  body  and  laminae  in  the  vermis  is 
perfect,  hence  the  name,  arbor  vitce,  which  is  appHed  to  them 
there.  In  the  anterior  cerebellar  notch  the  medullary  body 
divides  into  a  thick  superior  lamina  and  a  thin  inferior  lamina 
which  are  separated  by  a  transverse  furrow,  the  bottom  of 
which  constitutes  the  peak,  or  fastigium,  of  the  fourth  ventricle. 
The  inferior  lamina  is  the  inferior  medullary  velum,  already 
described;  this,  with  the  continuation  of  its  ependymal  epi- 
thelium, forms  the  roof  of  the  inferior  half  of  the  fourth  ventricle. 
The  superior  lamina  of  the  corpus  medullare  forms  the  three 
pairs  of  connecting  bands  (peduncles)  and  the  superior  medullary 
velum.     MeduUated  axones  make  up  the  entire  corpus  medullare 


BRACHIUM  CONJUNCTIVUM  287 

and  its  divisions.     We  study  these  axones  in  three  systems 
like  those  of  the  cerebrum: 

I.     Projection,  or  peduncular  fibers. 
II.     Commissural  fibers. 
III.     Association  fibers. 


I.  PROJECTION  FffiERS 

All  fibers  that  leave  the  cerebellum,  or  enter  it,  do  so  through 
the  brachia,  the  restiform  bodies  and  the  superior  medullary 
velum,  hence  these  are  composed  of  projection  fibers.  At  a 
higher  level  the  projection  fibers  are  contained  in  the  corpus 
medullar  e. 

Brachiixm  Conjunctivum  (Figs.  56, 102  and  103). — The  brach- 
ium  conjunctivum  (superior  peduncle)  is  the  innermost  of  the 
three,  at  its  origin  in  the  anterior  cerebellar  notch;  lateral  to  it, 
in  the  notch,  are  the  restiform  body  and  the  brachium  pontis; 
and,  in  the  angle  between  the  brachium  conjunctivum  and 
the  restiform  body,  is  the  vestibular  nucleus  of  Bechterew 
(the  upper  part  of  Deiters's  nucleus).  The  brachium  conjunc- 
tivum is  joined  to  its  fellow  of  the  opposite  side  by  the  superior 
medullary  velum  (velum  medullar e  superius).  The  brachium 
conjunctivum  contains  one  great  tract,  the  superior  cerehello- 
tegmental  fasciculus.  It  is  composed  chiefly  of  axones  of  the 
dentate  nucleus,  augmented  by  a  small  number  from  the 
nuclei  emboliformis,  globusus  and  fastigii.  This  tract  of 
fibers  partially  buries  itself  in  the  dorsal  area  of  the  pons,  then 
penetrates  the  mid-brain  and  decussates  ventral  to  the  inferior 
quadrigeminal  coJliculi.  It  ends  largely  in  the  opposite  red 
nucleus,  but  partly  in  the  thalamus  and  motor  nuclei  of  the 
mid-brain,  pons  and  medulla.  This  cerebello-tegmental  fasc- 
iculus of  the  brachium  conjunctivum  includes  a  diencephalic. 
a  mesencephalic,  a  pontine  and,  probably,  a  bulbar  part. 
It  forms  a  link  in  the  mechanism  coordinating  the  movements 
of  locomotion.  In  the  red  nucleus  this  path  is  relayed  to  the 
thalamus  by  the  ruhro-thalamic  tract  and  a  part  of  the  cerebello- 
tegmental  tract  enters  the  thalamus  directly,  on  the  same  side; 


288  THE   RHOMBENCEPHALON 

SO  this  path  may  also  conduct  afferent  impulses  from  the 
cerebellum  which  ultimately  reach  the  cortex  of  the  cerebrum. 

The  brachium  conjunctivum  contains  a  small  cerebello- 
petal  tract  which  appears  to  rise  in  the  terminal  nuclei  of  the 
optic  nerve  and  end  in  the  cerebellum.  According  to  Edinger 
such  a  tract  is  well  developed  in  fishes,  reptiles,  amphibians 
and  birds.  It  may  be  distinguished  as  the  optic  nucleo-cerehellar 
fasciculus. 

A  few  commissural  fibers  between  Bechterew's  nuclei  are 
found  in  the  cerebellar  end  of  the  brachium  conjunctivum,  and 
the  fila  lateralia  pontis  traverses  the  same  part  of  it.  The  fila 
lateralis  pontis  (taenia  pontis)  is  a  dissociated  bundle  of  the 
transverse  fibers  of  the  pons.  Rising  in  the  opposite  nucleus 
pontis,  it  winds  around  the  isthmus  to  the  brachium  con- 
junctivum; according  to  Horsley,  it  terminates  in  the  dentate 
nucleus.  The  commissural  fibers  connecting  Bechterew's  nuclei 
cross  from  one  brachium  to  the  other  through  the  superior 
medullary  velum. 

The  superior  medullary  velum  (Fig.  102)  arches  over  the 
fourth  ventricle  between  the  brachia  conjunctiva.  It  is  com- 
posed of  longitudinal  and  transverse  fibers.  One  distinct 
bundle,  derived  from  the  spinal  cord,  passes  through  it  to  the 
worm.  This  is  the  ventral  spino-cerebellar  fasciculus  of  Gowers. 
The  other  longitudinal  tract  is  the  tecto -cerebellar  fasciculus, 
which  rises  in  the  inferior  colliculus  of  the  quadrigeminal 
lamina  (tectum)  and  terminates  in  the  cerebellum.  It  connects 
the  olfactory  and  acustic  paths  with  the  great  center  of  coordi- 
nation. The  decussating  root-fibers  of  the  fourth  nerve  (troch- 
lear) course  transversely  through  it  and  also  the  commissural 
fibers  between  Bechterew's  nuclei. 

Brachium  Pontis  (Middle  Peduncle,  Figs.  56, 103, 107  and  122). 
■ — The  brachium  pontis  comes  from  the  pons,  of  which  it  forms 
the  basilar  transverse  fibers.  It  enters  into  the  medullary 
body  of  the  cerebellum  lateral  to  both  the  brachium  con- 
junctivum and  the  restiform  body.  According  to  Klimoff 
fibers  running  to  the  cerebellum  make  up  the  entire  brachium 
pontis.     These  are  axones  of  the  nucleus  pontis  and  nucleus 


RESTIFORM  BODY  289 

ponto-bulbaris,  the  opposite  ones.  Most  of  them  run  to  the 
cortex  of  the  cerebellar  hemisphere;  a  small  number  run  to  the 
vermis  cerebelli.  They  form  a  segment  in  the  indirect  efferent 
path  contained,  above  the  pons,  in  the  medial  and  lateral  fifths 
and  the  intermediate  bundle  of  the  basis  pedunculi.  By  far 
the  greater  number  of  fibers  in  the  brachium  pontis  are  crossed 
fibers. 

Possibly  there  are  in  the  brachium  pontis  axones  of  Purkinje's  or  the 
nuclear  cells  which  terminate  in  the  nuclei  pontis  on  both  sides  and  in 
the  nuclei  of  the  reticular  formation,  tractus  cerebello-tegmentalis  pontis. 

The  corpus  restiforme  (inferior  peduncle)  (Figs.  56,  103,  107 
and  122)  can  be  traced  to  the  upper  part  of  the  hemisphere  and 
worm.  Inferiorly  it  is  the  restiform  body  of  the  medulla 
oblongata.  It  enters  the  corpus  medullare  of  the  cerebellum 
in  front  of  the  dentate  nucleus  and  just  lateral  to  the  brachium 
conjunctivum.  The  bundles  of  component  fibers  are  very 
numerous:  (i)  The  dorsal  spino-cerehellar  fasciculus  (direct 
cerebellar  tract),  whose  origin  is  in  the  dorsal  nucleus  of  the 
cord  and  termination  in  the  superior  worm,  forms  its  central 
part.  This  is  the  tract  of  Flechsig.  (2)  The  external  arcuate 
fibers  of  the  medulla  (posterior  and  anterior)  form  its  free  sur- 
face. They  rise  in  the  nucleus  funiculi  gracilis,  nucleus  funiculi 
cuneati  and  nucleus  arcuatus  and  end  in  the  vermis  superior, 
the  posterior  on  the  same  and  the  anterior  on  the  opposite  side. 
(3)  A  bundle  from  the  lateral  nucleus  of  the  medulla,  the  reticulo- 
cerebellar  fasciculus,  to  the  cortex  of  the  cerebellum  on  the  same 
side.  (4)  The  olivo-cerebellar  fasciculus  rises  in  the  opposite 
inferior  olive,  chiefly,  but  partly  in  the  olive  of  the  same  side; 
it  terminates  in  the  cortex  of  the  vermis.  Some  authors  claim 
there  are  descending  fibers  in  this  bundle.  (5)  The  direct 
sensory  fasciculus  of  the  cerebellum  is  composed  of  root-fibers 
of  sensory  nerves,  especially  the  trigeminal  and  vestibular 
nerves.  It  is  closely  related  to  the  following  tract.  (6)  The 
nucleo-cerebellar  fasciculus  rises  in  terminal  nuclei  of  cranial 
nerves.  The  vestibular  fibers  of  tracts  five  and  six  terminate 
in  the  opposite  nucleus  fastigii;  other  fibers  of  the  restiform  body 
end  in  the  cerebellar  cortex.  The  restiform  body,  like  the 
19 


290  THE   RHOMBENCEPHALON 

brachium  pontis,  is  a  great  cerehello-petal  path.  Brachium  pontis 
connects  cerebellum  to  the  cerebrum;  restiform  body  joins  it 
to  the  spinal  cord,  the  medulla  and  the  sensory  cranial  nerves. 
The  cerebellum  correlates  all  the  impulses  arriving  by  the 
cerebello-petal  tracts  and  sends  out  its  coordinating  impulses 
through  the  cerehello-tegmental  system  of  fibers,  which  form  the 
brachium  conjunctivum  and  the  fastigio-bulbar  fasciculus  next 
to  be  described. 

In  the  cerebellar  end  of  the  restiform  body  there  runs  a  small 
tract  forming  the  bulbar  part  of  the  cerebello-tegmental  fibers. 
This  is  the  fastigio-bulbar  fasciculus.  Originating  in  the 
opposite  nucleus  fastigii  and  decussating  at  once,  it  descends 
chiefly  to  Deiter^s  nucleus,  but  some  of  its  fibers  end  in  the 
nuclei  of  motor  cranial  nerves.  It  constitutes  a  descending 
Unk  in  the  vestibular  arc  of  equilibrium. 

n.  COMMISSURAL  FffiERS 

The  cerebellar  hemispheres  are  joined  by  transverse  fibers, 
of  which  there  are  two  sets,  namely:  One  near  the  anterior 
end  of  the  worm  beneath  the  central  lobe  and  in  front  of  the 
nucleus  fastigii,  the  anterior  cerebellar  commissure.  This  is 
the  larger  of  the  two.  Its  fibers  diverge  anterior  to  the  dentate 
nucleus  and  through  the  medullary  laminae  reach  the  greater 
part  of  the  cerebellar  cortex.  The  posterior  cerebellar  commissure 
penetrates  the  medullary  core  of  the  vermis  posterior  to  nucleus 
fastigii  and  near  the  origin  of  the  medullary  lamina  of  the 
pyramid.  Its  fibers  radiate  posterior  to  the  dentate  nucleus 
to  reach  the  adjacent  cortex.  The  fastigial  commissure  has  been 
mentioned  as  connecting  the  two  roof-nuclei. 

m.  ASSOCIATION  FIBERS 

Limited  areas  of  cerebellar  cortex  are  richly  associated  to- 
gether as  pointed  out  in  the  description  of  the  cortical  gray 
substance;  but  there  appears  to  be  nothing  analogous  to  the 
long  association  fibers  found  in  the  cerebrum. 


EQUILIBRATION 


291 


Comparative  anatomy  shows  that  the  development  of  the  cerebellum  is 
proportional  to  the  equilibratory  needs  of  the  animal  (Edinger).     Animals 


Fig.  III. — Anterior  aspect  of  mid-brain,  pons  and  medulla.  (After  Morrises 

Anatomy.) 

a.  Anterior  perforated  substance,  b.  Corpus  mammillare.  c.  Cerebral  peduncle,  d. 
Ganglion  semilunare  (gasseri).  e.  Oblique  fasciculus,  f.  N.  hypoglossus  (XII).  g. 
Pjrramid.  h.  Decussation  of  pyramids,  i.  Insula,  j.  Olfactory  tract,  k.  Hypophysis. 
1.  N.  opticu.  (II).  m.  Optic  tract,  n.  Tuber  cinereum.  o.  N.  oculomotonus  (III). 
p.  Lateral  geniculate  body.  q.  N.  trochlearis  (IV).  r.  N.  Trigeminus  (M.  P.).  s.  N. 
trigeminus  (V).  t.  N.  abducens  (VI).  u.  Brachium  pontis.  v.  N.  facialis  (VII). 
w.  N.  intermedius.  x.  N.  acusticus  (VIII).  y.  N.  glossopharyngeus  (IX).  z.  N.  vagus 
(X).  aa.  N.  accessorius  (XI)  (spinal  accessory),     bb.  Cervical  I.     cc.  Cervical  II. 


without  locomotion  living  their  lives  attached  to  other  animals  or  to  stones, 
as  the  myxine,  have  no  cerebellum.     Swimming  animals  have  a  larger 


292  THE    RHOMBENCEPHALON 

cerebellum  than  members  of  the  same  order  which  live  on  land  (as  turtles) . 
The  cerebellum  is  larger  in  actively  swimming  fish  than  in  the  closely  allied 
but  inactive  forms  that  lie  much  of  the  time  flat  on  the  bottom.  The 
cerebellar  hemispheres  and  lateral  nuclei  (dentate,  emboliform  and  globose) 
are  represented  in  very  low  vertebrates;  but  the  hemispheres  are  not 
differentiated  until  a  connection  is  established  with  the  cerebrum  (as  in 
mammals)  and  the  nucleus  fastigii  is  not  well  developed  except  in  birds  and 
mammals,  though  it  is  indicated  in  the  edible  turtle  (chelone  midas).  In 
low  vertebrates  there  is  but  one  cerebellar  peduncle,  the  fibers  of  which 
diverge  frontally  and  caudally  in  the  pons.  All  cerebello-petal  fibers 
Edinger  calls  the  nucleo-cerebellar  tract,  because  they  rise  in  the  nuclei  (ter- 
minal) of  the  brain  and  spinal  cord.  All  cerebello-fugal  fibers  constitute 
the  cerebello-tegmental  tract,  as  they  terminate  chiefly  in  the  tegmentum 
of  the  mid-brain,  pons  and  medulla  (Brain,  Vol.  29). 

RHOMBENCEPHALON 
SECTION  n.    THE  PONS  (VAROLH) 

The  pons  and  medulla  form  the  ventral  part  of  the  rhomben- 
cephalon, the  cerebellum  being  its  dorsal  portion.  By  a  trans- 
verse indentation  of  its  roof,  the  posterior  brain-vesicle  is  par- 
tially divided  into  an  upper  vesicle,  the  metencephalon,  and  a 
lower  vesicle,  the  myelencephalon;  the  latter  is  the  embryonic 
medulla,  the  former  gives  rise  to  the  cerebellum  and  the  pons. 
The  pons  is  developed  from  the  floor  of  the  metencephalon 
(Fig.  104).  It  is  so  named  because  it  forms  the  connecting  link 
or  bridge  between  the  mid-brain  above  and  the  cerebellum  and 
medulla  oblongata  below;  between  the  medulla  and  cere- 
bellum and  between  the  two  cerebellar  hemispheres  (Fig.  iii). 

In  shape  the  pons  is  roughly  cylindrical.  It  has  a  broad 
basal  or  ventral  part,  the  pars  basilaris  pontis,  and  a  narrower 
dorsal  portion,  the  pars  dorsalis  pontis  (Fig.  113). 

Size. — The  pons  is  about  2.5  cm.  (i  inch)  long.  It  is  a  little 
broader  than  long,  and  measures  2.5  cm.  dorso-ventrally. 

Position. — It  rests  in  the  anterior  end  of  the  groove  which 
extends  from  the  foramen  magnum  to  the  dorsum  sellae,  and 
lies  between  and  ventral  to  the  hemispheres  of  the  cerebellum. 
Superiorly,  it  joins  the  mid-brain;  and,  below,  it  is  continuous 
with  the  medulla  oblongata. 


SURFACE   OF  PONS  293 

Surfaces  of  the  Pons.— The  pons  has  four  surfaces,  viz., 
superior  (attached);  inferior  (attached);  anterior  (free),  and 
posterior  (partially  free) ;  and  two  borders,  namely,  right  and 
left  lateral,  continuous  with  the  brachium  pontis  of  the  cere- 
bellum. 

The  superior  and  inferior  surfaces  are  made  by  section,  and 
are  directly  continuous  with  mid-brain  above  and  the  medulla 
below. 

Anterior  Surface  (tuber  annulare). — The  anterior  surface 
of  the  pons  (Fig.  in)  looks  forward  and  slightly  downward  and 
rests  on  the  sphenoid  bone  behind  the  dorsum  sellae.  It  is 
divided  into  lateral  halves  by  the  sulcus  basilaris,  containing  the 
basilar  artery;  and  is  bounded  laterally  by  a  sagittal  plane 
cutting  the  root  of  the  trigeminal  nerve.  Vertically  the  sur- 
face is  slightly  convex,  and  is  markedly  so  from  side  to  side. 
It  shows  transverse  striations,  which  converge  laterally,  due  to 
the  fibers  that  form  it  and  enter  the  brachia  pontis  of  the  cere- 
bellum. The  fibers  of  the  anterior  surface  are  not  exactly 
transverse  in  direction.  Those  at  the  superior  end  of  the  pons 
bend  downward  and  form  a  rounded  margin,  which  covers  the 
lower  part  of  the  bases  pedunculi  of  the  mid-brain;  at  the 
inferior  extremity  of  the  pons,  the  fibers  are  convex  downward 
and  partially  conceal  the  pyramids  of  the  medulla  oblongata. 
Just  medial  to  the  root  of  the  trigeminal  nerve  there  is  an  oblique 
bundle  of  fibers  called  the  fasciculus  ohliquus  pontis.  This 
fasciculus  rises  in  the  medulla  oblongata  from  the  nucleus 
ponto-bulbaris  (the  tail  end  of  the  nucleus  pontis) ;  it  runs  up- 
ward across  the  ponto-medullary  groove,  between  the  facial  and 
intermediate  nerves;  at  the  level  of  the  trigeminal  root  it  bends 
sharply  toward  the  median  line,  mingles  with  the  transverse 
fibers  of  the  pons  and,  with  them,  enters  the  opposite  brachium 
pontis.  Like  other  fibers  of  the  anterior  surface  of  the  pons, 
those  of  the  fasciculus  obliquus  terminate  in  the  cerebellar 
cortex.  The  two  roots  of  the  fifth  nerve  (trigeminal)  are  at- 
tached to  the  lateral  border  (Henle)  of  this  surface,  a  little  above 
the  middle. 

The  posterior  surface  of  the  pons  is  concealed  by  the  cere- 


294 


THE   EHOMBENCEPHALON 


bellum  (Fig.  114).  It  is  free  in  its  middle  part,  where  it  forms  the 
floor  of  the  superior  half  of  the  fourth  ventricle  (Fig.  112).  The 
ventricular  area  of  the  posterior  surface  is  completely  concealed 
by  the  superior  medullary  velum.     If  examined,  it  is  found  to  be 


Fig.  112. — Dorsal  surface  of  pons  and  medulla.     (Morrises  Anatomy  modified 

from  Spalteholz.) 
a.  Median  sulcus,  b.  Superior  fovea,  c.  Limiting  sulcus,  d.  Medial  eminence,  e. 
Striae  medullares.  f.  Inferior  fovea,  g.  Nucleus  funiculi  cuneati.  h.  Taenia  of  fourth 
ventricle,  i.  Area  postrema.  j.  Nucleus  funiculi  gracilis  (clava).  k.  Posterior  median 
fissure.  1.  Aquaeductus  cerebri,  m.  Nucleus  incertus.  n.  Locus  caeruleus.  o.  CoUiculus 
facialis  et  nucleus  abducentis.  p.  Nucleus  N.  cochlearis  (tuberculum  acusticum).  q. 
Area  acustica  (nucleus  vestibularis),  r.  Nucleus  intercalatus.  s.  Trigonum  N.  hypoglossi. 
t.  Ala  cinerea.     u.  Funiculus  separans.     v.  Obex. 


divided  into  lateral  halves  by  a  median  longitudinal  groove. 
Each  half  presents  in  its  posterior  part  a  rounded  eminence, 
the  colliculus  facialis,  which  flanks  the  median  furrow  and  is  in 
turn  bounded,  laterally,  by  a  linear  valley,  the  sulcus  limitans, 
lying  near  the  brachium  conjunctivum  cerebelli  and  parallel 


STRUCTURE   OF   PONS  295 

with  it.  The  inferior  end  of  the  valley  is  called  the  fovea 
superior;  its  upper  part  has  a  bluish  tint,  due  to  underlying 
pigmented  cells,  and  is  called  the  locus  cceruleus.  Attached 
Area. — ^Lateral  to  this  ventricular  area  the  posterior  surface  of 
the  pons  is  attached  to  the  restiform  body  and  the  conjoined 
arms  of  the  cerebellum.  The  restiform  bodies  enter  the  surface 
at  the  lower  end  of  the  pons  and  then  bend  backward  into  the 
cerebellum;  while  the  brachia  conjimctiva,  in  their  course  up 
to  the  cerebrum,  partly  imbed  themselves  in  the  lateral  part 
of  the  posterior  surface  and  form  the  walls  of  the  fourth  ventricle. 
The  lateral  fillet  issues  from  this  surface  just  lateral  to  the  brach- 
ium  conjunctivum.  It  runs  obliquely  across  the  upper  end 
of  the  brachium  to  the  inferior  colliculus  of  the  corpora  quad- 
rigemina,  and  produces  a  flat  striated  ridge,  which  may  be  seen 
easily  in  a  well-hardened  specimen.  A  second  bundle  of  fibers 
issues  from  the  attached  area  of  the  posterior  surface  of  the 
pons  and  winds  upward  over  the  brachium  conjunctivum: 
it  is  the  ventral  spino-cerehellar  fasciculus.  Passing  over  the 
brachium,  it  enters  the  superior  medullary  velum  and  terminates 
in  the  cortex  of  the  vermis  cerebelli. 

Structure  of  the  Pons. — The  pons  is  composed  of  transverse 
and  longitudinal  white  fibers  and  of  gray  matter.  The  trans- 
verse fibers  are  found  chiefly  in  the  basilar  portion  of  the  pons; 
the  longitudinal,  in  both  the  basilar  and  the  dorsal  parts.  The 
basilar  longitudinal  intersect  the  deep  transverse  fibers  of  the 
pars  basilaris. 

TRANSVERSE  FIBERS  OF  PONS 

The  transverse  fibers  form  two  consecutive  layers  in  the  ponSy 
viz.,  the  basilar,  and  the  dorsal  layers.  They  lie  one  upon 
another.  The  former  are  situated  in  the  basilar  part  of  the 
pons,  the  latter  in  the  dorsal  part  (Figs.  113-118). 

Basilar  Fibers. — The  superficial  transverse  fibers  are  an- 
terior in  position  and  form  a  thin  compact  layer  constituting 
the  anterior  surface  of  the  pons  (Fig.  113).  They  are  not  inter- 
sected by  longitudinal  fibers;  but,  otherwise,  are  like  the  deeper 
transverse  fibers  of  the  pars  basilaris  pontis. 


296  THE    RHOMBENCEPHALON 

Deep  Transverse  Fibers  of  Pars  Basilaris. — These  form  a 
thick  lamina  posterior  to  the  superficial  transverse  fibers  and 
in  contact  with  the  superficial  lamina.  They  are  intermingled 
with  longitudinal  fibers  from  the  bases  pedunculi,  viz.,  the 
pyramidal,  fronto-pontal,  temporo-pontal  and  intermediate 
tracts  (Figs.  113-118).  In  the  meshes  between  the  inter- 
secting fibers  is  a  large  mass  of  gray  matter  on  either  side  called 
the  nucleus  ponds.  The  deep  and  superficial  transverse  fibers 
of  the  pars  basilaris  pontis  form  the  brachia  pontis  cerebelli. 
Their  origin  is  found  in  the  opposite  nucleus  pontis  and  nucleus 
ponto-bulbaris.  They  continue  the  indirect  efferent  path  from 
the  termination  of  the  fronto-pontal.  temporo-pontal  and  inter- 
mediate tracts  in  the  nuclei  pontis  and  ponto-bulbaris  to  the 
cerebellar  cortex  of  the  opposite  side. 

In  connection  with  the  superficial  and  deep  transverse  fibers 
in  the  basilar  part  of  the  pons  there  should  be  mentioned  an 
independent  strand,  the  fila  lateralia  pontis,  which  is  situated 
at  the  upper  border  of  the  pons  and  buried  more  or  less  in  the 
isthmian  furrow  between  the  pons  and  mid-brain.  It  is  called 
by  Henle  the  taenia  pontis.  According  to  Sir  Victor  Horsley  it 
rises  from  the  nucleus  pontis  just  ventral  to  the  interpeduncular 
ganglion  and,  winding  round  the  isthmus,  enters  the  cere- 
bellum through  the  brachium  conjunctivum.  Its  destination 
is  probably  the  nucleus  dentatus  and  nucleus  fastigii  (Brain, 
Vol.  29,  No.  113). 

Dorsal  Fibers. — The  transverse  fibers  of  the  pars  dorsalis 
pontis  (Fig.  114)  compose  a  thin  layer  on  the  dorsum  of  the 
basilar  transverse  fibers;  they  belong  to  the  formatio  reticularis. 
This  transverse  lamina  is  present  only  in  the  inferior  part  of  the 
pons.  It  is  called  the  corpus  trapezoideum.  Its  fibers  inter- 
sect those  of  the  medial  fillet. 

The  trapezoid  body  (corpus  trapezoideum)  lies  in  the  dorsal 
part  of  the  pons,  next  the  boundary  between  the  pars  basilaris 
and  the  pars  dorsalis  pontis.  Its  fibers  rise  chiefly  from  the 
ventral  nuclei  of  the.  cochlear  nerve  and,  after  decussating  in  the 
raphe,  are  continued  up  in  the  lateral  fillets  to  the  inferior 
quadrigeminal  colliculi  and  brachia.     A  few  fibers  join  the  tract 


LONGITUDINAL  TRACTS  OF  PONS  297 

directly  from  the  cochlear  nerve.  The  nuclei  of  the  trapezoid 
body,  of  the  superior  olive,  etc.  (olivary  group) ,  form  relays  for 
a  number  of  its  fibers.  The  corpus  trapezoideum  with  the 
medullary  striae  and  the  lateral  fillet  which  is  the  continuation 
of  both,  form  the  second  stage  in  the  auditory  conduction 
path;  and  the  auditory  impulses  are  continued  (a)  through  the 
brachium  quadrigeminum  inferius  and  (b)  the  acustic  radiation 
to  the  temporal  cortex  (Figs.  116,  118  and  119). 

LONGITUDINAL  FIBERS  OF  PONS 

The  longitudinal  fibers  of  the  pons  are  arranged  in  two  dis- 
tinct groups,  viz.,  the  basilar  or  anterior  and  the  dorsal  or 
posterior  (Figs.  113-118). 

The  basilar  longitudinal  fibers  are  situated  in  the  pars 
hasilaris  pontis  (Figs.  113-118).  Four  fasciculi  make  them  up. 
They  are  the  four  efferent  tracts  of  the  basis  pedunculi.  The 
fronto-pontal,  temporo-pontal  and  intermediate  tracts  termi- 
nate chiefly  in  the  nucleus  pontis.  The  pyramidal  fibers  run 
from  the  middle  three-fifths  of  each  basis  pedunculi  down 
through  the  basilar  transverse  layer  of  the  pons  and  the  pyra- 
mids of  the  medulla  oblongata.  Together  with  the  above 
cerebro-pontal  tracts  they  form  a  thick  bundle  on  either  side 
of  the  median  line,  which  presses  down  the  superficial  trans- 
verse fibers  and  produces  the  sulcus  hasilaris.  The  nucleus 
pontiSj  one  on  either  side,  is  situated  among  the  pyramidal 
fibers.  The  .pyramidal  tracts  diminish  in  size  during  their 
descent  because  of  the  fibers  which  leave  them  to  decussate  and 
end  in  the  nuclei  of  motor  cerebral  nerves. 

The  Dorsal  Longitudinal  Fibers. — These  are  contained  in 
the  pars  dorsalis  pontis  in  the  formatio  reticularis  (Figs.  113- 
118).  They  are  in  and  dorsal  to  the  corpus  trapezoideum 
and  lie  in  the  floor  of  the  fourth  ventricle  where  they  are 
intermingled  with  the  reticular  gray  substance.  They  do  not 
form  a  compact  layer  but  are  collected  into  a  number  of  dis- 
tinct strands  of  which  the  larger  are  visible  to  the  naked  eye 
in  Weigert-Pal  sections.     The  dorsal  longitudinal  fibers  are 


298  THE  RHOMBENCEPHALON 

mingled  with  many  transverse  and  oblique  fibers,  and  thus 
there  is  produced  the  netlike  arrangement  suggesting  the  name, 
formatio  reticularis.  The  formatio  reticularis  of  the  pons  is 
continued  down  from  the  tegmentum  of  the  mid-brain  and 
comprises  the  tegmental  region  of  the  pons.  The  gray  matter 
in  the  meshes  of  this  network  which  is  continued  up  from  the 
medulla  contains  the  nuclei  of  the  fifth,  sixth  and  seventh 
cerebral  nerves  and  a  part  of  the  nucleus  of  the  eighth  nerve, 
and  also  the  nuclei  of  the  formatio  reticularis,  viz.,  the  nucleus 
centralis  superior,  medius  and  inferior,  and  the  nucleus  lateralis 
medius.  In  the  formatio  reticularis  are  the  bundles  or  tracts 
of  fibers  that  constitute  the  dorsal  longitudinal  fibers  of  the  pons. 
These  tracts  are  as  follows:  medial  fillet,  lateral  fillet,  ventral 
spino-cerebellar  fasciculus,  spino-tectal  fasciculus,  spino- 
thalamic fasciculus,  medial  longitudinal  fasciculus,  gustatory 
fasciculus,  spinal  tract  of  the  trigeminal  nerve;  mesencephalic 
root  of  the  trigeminal  nerve,  tecto-spinal  fasciculi-anterior 
and  lateral,  reticulo-spinal  fasciculi-anterior  and  lateral, 
thalamo-olivary  fasciculus,  thalamo  spinal  fasciculus,  rubrof 
spinal  fasciculus  and  the  dorsal  longitudinal  fasciculus  o- 
Schiitz  in  the  gray  substance.  The  brachium  conjunctivum 
cerebelli  is  partly  buried  in  the  dorsal  region  of  the  pons,  so 
its  position  and  relations  should  be  noted  here  (for  descrip- 
tion see  p.  287).  The  ventral  spino-cerebellar  fasciculus  and 
the  spinal  tract  of  the  trigeminal  (or  fifth)  nerve  are  the  only 
tracts  not  already  considered  in  our  study  of  the  tegmental 
region  of  the  mid-brain,  p.  152. 

I.  The  medial  fillet  {lemniscus  medialis,  Figs.  11 3-1 18) 
is  a  large  bundle  of  fibers  that  runs  through  the  pons  next  the 
median  plane.  In  the  lower  part  of  the  pons  it  lies  within  and 
dorsal  to  the  trapezoid  body.  Its  origin  is  found  on  the 
opposite  side  in  the  nucleus  funiculi  gracilis  and  nucleus  fu- 
niculi cuneati  and  in  the  terminal  nuclei  of  common  sensory 
cerebral  nerves  (Fig.  125).  It  conducts  impulses  of  the  tactile, 
static  and  muscular  senses.  In  the  mid-brain  it  gives  off  the 
superior  fillet  {lemniscus  superior)  which  terminates  in  the 
superior    quadrigeminal    colliculus.     The    medial    fillet   ends 


ACUSTIC  PATH 


299 


in  the  lateral  nucleus  of  the  thalamus  (Fig.  54).  Interrup- 
tion of  the  medial  lemniscus  causes  ataxia  on  the  opposite 
side. 

2.  Lateral  Fillet  {lemniscus  lateralis)  .—The  lateral  fillet 
forms  a  link  in  the  special  sense,  auditory  path  (Fig.  119).  As 
stated  on^p.  297  it  is  but  the  longitudinal  continuation  of  the 
corpus  trapezoideum  and  the  medullary  striae.  It  takes  form 
near  the  middle  of  the  pons,  where  the  fibers  of  the  trapezoid 
body  bend  upward  to  a  longitudinal  direction;  and  it  runs  just 
lateral  to  the  medial  fillet  (Figs.  113  and  115).  Very  soon  it  be- 
comes separated  from  the  medial  fillet  by  the  brachium  con- 
junctivum  of  the  cerebellum.  It  runs  dorso-medially  over 
the  conjoined  brachium  to  the  inferior  colliculus  of  the  corpora 
quadrigemina,  where  a  few  of  its  fibers  end;  but  the  greater 
number  are  continued  through  the  brachium  inferius  to  the 
medial  geniculate  body.  The  chief  origin  of  the  lateral  fillet 
is  found  in  the  opposite  cochlear  nuclei,  though  some  of  its 
fibers  rise  in  the  nucleus  of  the  corpus  trapezoideum,  the 
superior  olivary  nucleus,  and  the  nucleus  of  the  lateral  fillet, 
which  constitute  partial  relays  in  the  auditory  path.  It  is 
also  true  that  a  few  fibers  enter  the  lateral  fillet  from  the 
cochlear  nuclei  and  nerve  of  the  same  side;  they  are  supposed 
to  decussate  near  or  in  the  quadrigeminal  bodies  and  terminate 
in  the  opposite  inferior  colliculus.  Destruction  of  the  lateral 
fillet  causes  deafness  in  the  opposite  ear. 

The  spino-thalamic,  spino-tectal  and  ventral  spino-cerebellar 
fasciculi  form  one  compound  funiculus  from  the  spinal  cord  up 
to  the  middle  of  the  pons;  this  is  the  tract  of  Gowers,  first  de- 
scribed in  1897.  At  the  level  of  the  root  of  the  trigeminal  nerve 
it  divides  into  a  bundle  going  to  the  cerebellum  and  parts 
going  to  the  tectum  (both  coUiculi)  and  to  the  thalamus. 

3.  The  spino-thalamic  tract  occupies  the  lateral  part  of 
the  formatio  reticularis  where  it  forms  a  loose  strand  (Figs. 
113-118).  As  already  stated,  it  rises  in  the  spinal  cord  from 
the  basal  gray  substance  of  the  anterior  columna  and  from 
the  terminal  nuclei  of  common  sensory  cerebral  nerves  in  the 
medulla   and  pons.     The   spino-thalamic   tract   ends   in   the 


300  THE   RHOMBENCEPHALON 

lateral  nucleus  of  the  thalamus.     It  conducts  impulses  of  the 
tactile,  pain  and  temperature  senses. 

4.  Those  fibers  of  Gower^s  tract  that  end  in  the  inferior 
and  superior  colliculi  of  the  tectum  constitute  the  spino- 
tectal fasciculus.  It  probably  carries  tactile  pain  and  tem- 
perature impulses  which,  however,  do  not  excite  the  correspond- 
ing sensations,  but  set  up  the  proper  reflexes  in  the  tectum. 

5.  The  ventral  spino-cerebellar  fasciculus  is  the  third 
bundle  of  Gowers^  tract.  Like  other  parts  of  Gowers'  tract, 
it  rises  from  the  basal  part  of  the  anterior  column  of  gray 
substance  in  the  cord  and  from  terminal  nuclei  of  common 
sensory  cranial  nerves.  The  ventral  spino-cerebellar  fasciculus 
terminates  in  the  cortex  of  the  superior  vermis,  largely  on  the 
opposite  side.  It  accompanies  the  spino-thalamic  tract  as 
far  as  the  root  of  the  trigeminal  nerve;  bending  backward  at 
that  level,  it  winds  over  the  dorso-lateral  surface  of  the  brachium 
conjunctivum  and  continues  through  the  superior  medullary 
velum  to  the  vermis. 

A  small  strand  of  large  fibers  diverges  from  the  ventral 
spino-cerebellar  fasciculus  in  the  pons,  and  enters  the  cerebellum 
through  the  caudal  half  of  the  brachium  pontis;  it  terminates 
also  in  the  anterior  cortex  of  the  superior  vermis.  This 
bundle  has  been  described  by  G.  B.  Pellizzi  as  an  intermediate 
spino-cerebellar  fasciculus,  because  in  the  cord  it  ascends  be- 
tween the  ventral  and  dorsal  fasciculi. 

The  ventral  spino-cerebellar  tract  probably  carries  tactile, 
pain  and  temperature  impulses  for  the  purpose  of  exciting 
reflex  coordinating  impulses  in  the  cerebellum;  but  these 
impulses  may  reach  the  centers  of  consciousness  and  evoke 
their  proper  sensations.  The  tract  thus  belongs  to  the  in- 
direct sensory  path  (through  the  cerebellum).  From  the 
cerebellar  cortex  the  path  is  continued  by  the  axones  of  Purk- 
inje's  cells  to  the  nucleus  dentatus,  whence  the  brachium  con- 
junctivum completes  it  up  to  the  opposite  red  nucleus  and 
thalamus.  The  ventral  spino-cerebellar  and  the  spino-thalamic 
and  spino-tectal  tracts  are  the  chief  bundles  of  a  spino-en- 
cephalic  system  of  fibers  which  terminates  very  largely  in  the 


GREAT  REFLEX  TRACT 


301 


cerebellum,  tectum  and  thalamus,  but  also  sends  fibers  to 
the  nucleus  lateralis  inferior  and  other  reticular  nuclei,  to  the 
substantia  nigra,  to  the  nucleus  ruber,  the  nucleus  hypo- 
thalamicus,  and  the  corpus  striatum. 

6.  The  medial  (posterior)  longitudinal  bundle  (fasciculus 
longitudinalis  medialis)  (Figs.  11 3-1 18)  runs  next  the  median 
plane  and  just  under  the  ventricular  gray  matter  in  a  position 
similar  to  the  one  it  occupies  in  the  mid-brain  (Figs.  59  and  60), 


Fig.  113. — Superior  section  of  the  pons.     Natural  color.     {Original.) 

a.  Beginning  of  decussation  of  Jbrachium  conjunctivum.  b.  Formatio  reticularis.  c. 
Brachium  conjunctivum.  d.  Medial  longitudinal  bundle,  e.  Fourth  ventricle,  f. 
Superior  medullary  velum,  g.  Descending  root  of  sth  n.  h.  Thalamo-olivary  tract,  i. 
Lateral  fillet,  j.  Medial  fillet,  k.  Long,  fibers  from  basis  pedunculi.  1.  Superficial  trans- 
verse fibers,     m.  Nucleus  pontis.     n.  Deep  transverse  fibers  of  pars  basilaris  pontis. 

see  p.  152.  It  is  in  the  pontine  portion  of  this  bundle  that 
the  fibers  from  the  oculomotor  nucleus  pass  to  the  genu  of  the 
facial  nerve,  ultimately  to  innervate  the  frontalis,  corrugator 
and  orbicularis  oculi;  it  is  in  the  pons  that  fibers  from  the 
abducent  nucleus  join  this  bundle  and  run  upward  through  it 
to  the  oculomotor  nucleus  of  the  opposite  side  and  make  pos- 
sible the  conjugate  movements  of  the  eyeballs;  it  is  also  here 
that  fibers  which  rise  in   the  hypoglossal  nucleus  leave  the 


302  THE   RHOMBENCEPHALON 

longitudinal  bundle  and  enter  the  facial  nerve  at  the  genu  to 
be  distributed  by  way  of  the  facial  to  the  orbicularis  oris.  As 
in  the  mid-brain  the  longitudinal  bundle  includes  the  two 
functional  tracts,  the  descending  strand  and  the  ascending 
strand. 

Such  connections  as  are  described  above  are  claimed  by 
Duval  and  Laborde,  and  by  Mendel,  and  they  afiford  explana- 
tions of  well-known  phenomena;  but  no  one  has  actually  traced 
these  fibers  either  by  myelenization  or  degeneration.  On  the 
other  hand,  Harman  claims  that  the  nerve  supply  of  the  facial 
muscles  above  the  orbit  is  derived  from  the  superior  part  of 
the  facial  nucleus;  and  the  nucleus  of  the  facial  nerve  innervates 
all  the  facial  muscles,  according  to  G.  Elliot  Smith.  Further- 
more, Schafer  and  Swimington,  and  E.  H.  Eraser  deny  the 
existence  of  fibers  running  from  the  abducent  nucleus  to  the 
nucleus  of  the  oculomotor  nerve  on  the  opposite  side. 

7.  The  gustatory  fasciculus  (Figs.  11 5- 118)  runs  upward 
through  the  pons  close  to  the  fourth  ventricle.  Imbedded  in 
the  gelatinous  gray  substance  in  the  medulla,  it  ascends  just 
ventral  to  it  in  the  pons  between  the  gray  substance  and  the 
thalamo-olivary  fasciculus.  It  rises  in  the  nucleus  of  the  soli- 
tary tract  and  terminates  in  the  lateral  nucleus  of  the  thalamus, 
as  stated  on  p.  161. 

8.  The  roots  of  the  trigeminal  nerve  are  both  present  in 
the  upper  half  of  the  pons;  below  the  middle  only  the  spinal 
tract  is  found.  The  spinal  tract  of  the  trigeminal  nerve  runs 
along  the  border  of  the  reticular  formation  just  lateral  to  its 
own  nucleus  and  ventro-medial  to  brachium  conjunctivum 
and  restiform  body.  It  is  composed  of  T-branched  axones 
which  enter  the  pons  as  the  sensory  root  of  the  trigeminal 
nerve;  its  origin  is  within  the  semilunar  ganglion.  The  as- 
cending rami  terminate  in  the  mesencephalic  nucleus  of  the 
fifth  nerve,  while  the  descending  rami  end  in  the  nucleus  of 
the  spinal  tract  of  the  trigeminal  nerve  all  the  way  down  to 
the  second  cervical  segment  of  the  cord. 

The  mesencephalic  root  of  the  trigeminal  nerve  has  been 
described   on   p.  239.     Where   both   roots    are  present,    the 


TECTAL  AND  RETICULAR  TRACTS  303 

mesencephalic  root  and  its  nucleus  are  medial  to  the  spinal 
tract.  The  mesencephalic  root  bends  forward  at  the  middle 
of  the  pons  and  enters  the  trigeminal  nerve. 

9.  The  tecto-spinal  tracts  are  the  anterior  and  the  lateral, 
described  on  pp.  155,  156  and  233. 

Anterior  Tecto-spinal  Fasciculus.— This  ocular-reflex  bundle 
is  continued  from  the  mid-brain  down  through  the  pons  in 
nearly  the  same  relative  position.  Diverging  a  little  from  the 
medial  longitudinal  bundle  as  it  descends  through  the  pons,  it 
is  located  in  the  formatio  reticularis  a  short  distance  ventro- 
lateral from  it.  The  anterior  tecto-spinal  bundle  can  be 
recognized  in  normal  adult  tissue  only  in  the  dorsal  tegmental 
decussation  (Meynerti)  of  the  mid-brain;  lower  down  it  can 
be  distinguished  from  the  surrounding  tissues  by  degeneration 
and  medullation  but  in  no  other  way  (Fig.  113).  Having  given 
fibers  to  the  oculomotor  and  trochlear  nuclei  above,  it  sends 
fibers  to  the  nucleus  of  the  abducent  nerve  at  this  level,  and 
perhaps  to  other  pontine  nuclei  (see  Mid-brain,  p.  155). 

The  lateral  tecto-spinal  fasciculus  descends  from  the  tectum 
of  the  mid-brain  on  the  side  of  its  origin;  it  is  a  direct  tract.  It 
proceeds  through  the  pons  in  the  lateral  part  of  the  reticular 
formation,  in  company  with  the  thalamo-spinal  and  rubro- 
spinal tracts.     It  terminates  in  motor  nuclei  (Figs.  11 5-1 18). 

10.  The  reticulo-spinal  fasciculi,  described  in  the  mid-brain 
(p.  154-5)  are  largely  reinforced  in  the  pons  by  the  middle 
lateral  and  the  three  central  nuclei  of  the  reticular  formation, 
all  of  which  are  located  in  the  pons.  They  are  association  tracts 
between  the  reticular  nuclei  of  the  brain-stem  and  the  gray 
matter  of  the  cord  (Figs.  115-118). 

The  anterior  reticulo-spinal  fasciculus,  the  uncrossed  tract, 
is  a  part  of  the  medial  longitudinal  bundle.  Its  course  is  along 
the  median  plane  just  in  front  of  the  ventricular  gray  substance* 

The  lateral  reticulo-spinal  fasciculus  is  made  up  of  crossed 
axones  from  the  reticular  nuclei  which,  upon  entering  the 
tract,  divide  into  short  ascending  and  long  descending  rami. 
By  degeneration  it  can  be  traced  through  the  lateral  part  of  the 
reticular  formation  of  the  pons;  it  is  not  a  compact  tract. 


304 


THE   RHOMBENCEPHALON 


II.  Rubro-spinal  Fasciculus  of  Monakow. — In  the  mid-brain 
we  have  traced  this  tract  from  the  red  nucleus  through  the 
ventral  tegmental  decussation  (Foreli)  to  the  opposite  side 
where  it  mingles  with  the  lateral  fillet  down  near  the  isthmus 
(Figs.  59  and  60).  It  occupies  the  same  position  in  the  upper 
half  of  the  pons;  it  is  close  to  the  posterior  surface  of  the  corpus 
trapezoideum  in  the  lower  part  of  the  pons  (Figs.  113-118). 
In  the  gray  crescent  of  the  spinal  cord  the  rubro-spinal  tract 


CoUiculus  facialis 
Nucleus  globosus  |_    Nucleus  fastigii 
Nucleus' emboliformis ' 
Hilus  of  nuc.  dentatus 
Nuc.  of  Bechterew 
Nuclei  of  5  th  nerve 


Nucleus  of  abducent  n. 


Medial  longitudinal 
bundle 


Tractus  spinalis  N.  trigemini 


Nucleus  of  facial  n. 
Formatio  reticularis 


Superior  olivary  nucleus 

"^         Transverse  fibers  to  brachium  pontis 
Pyramidal  tract 
Trapezoid  body  and  medial  fillet 

Fig.  114. — Inferior  section  of  the  pons  together  with  the  cerebellum.     Natural 

color.     (Original.) 

ends.  Its  function  is  coordination  of  the  movments  of  locomo- 
tion (Horsley). 

A  number  of  axones  from  the  red  nucleus,  both  crossed  and 
uncrossed,  terminate  in  the  reticular  formation  of  the  pons  and 
medulla,  the  fasciculus  rubro-reticularis;  others  are  said  to  end 
in  the  nucleus  of  the  lateral  fillet,  the  fasciculus  rubro-laquearis. 

12.  The  thalamo-oHvary  fasciculus  (or  olivary  fasciculus) 
is  regarded  by  many  as  an  ascending  tract,  but  the  weight  of 
evidence  at  present  is  in  favor  of  a  descending  course.  Rising 
in  the  thalamus  (?)  and  descending  through  the  mid-brain  it 


NUCLEUS   PONTIS 


305 


enters  the  center  of  the  reticular  formation  of  the  pons,  hence 
the  name  central  tegmental  tract  (Fig.  115).  It  runs  dorsal  to  the 
medial  fillet  and  the  corpus  trapezoideum  in  the  lower  part  of 
the  pons,  just  medial  to  the  superior  olivary  nucleus.  It 
terminates  in  the  inferior  olive.  Through  the  pons  and  upper 
medulla,  it  is  visible  as  a  large  and  loose  fasciculus. 

13.  The  Fasciculus  Thalamo -spinalis. — The  thalamo-spinal 
bundle  descends  with  the  rubro-spinal  tract  through  the  lateral 
part  of  the  reticular  formation  in  the  pons  and  medulla  to  the 
lateral  column  of  the  spinal  cord  (J.  S.  Collier).  It  terminates 
in  the  gray  substance  of  the  cord,  probably  giving  off  collaterals 
to  corresponding  nuclei  in  the  brain-stem  (Figs.  115-118). 

14.  The  dorsal  longitudinal  bxmdle  of  Schiitz  {fasciculus 
longitudinalis  dor  sails,  Figs.  115  and  117)  descends  through  the 
ventricular  gray  substance  of  the  pons,  just  beneath  the  medial 
eminence  of  the  ventricular  floor.  Rising  in  the  central  gray 
matter  and  nucleus  tegmenti  dorsalis  of  the  mid-brain  it  is 
said  to  establish  connections  with  all  cranial  nerve  nuclei 
(Villiger).  It  constitutes  important  links  in  the  olfactory 
reflex  mechanisms. 

GRAY  MATTER  OF  THE  PONS 

In  the  pons  gray  matter  is  found  in  two  situations:  (i)  In 
the  interstices  between  the  transverse  and  longitudinal  fibers 
of  the  pars  basilaris  pontis,  the  nuclei  pontis;  and  (2)  in  the  pars 
dorsalis  pontis,  where  we  find  the  gelatinous  gray  sheet  im- 
mediately beneath  the  ventricle  and  the  scattered  nuclei  in  the 
reticular  formation. 

The  nucleus  pontis  is  a  mass  of  gray  matter  on  either  side 
the  raphe,  containing  the  bodies  of  large  multipolar  nerve  cells 
whose  axones  run  through  the  brachium  pontis  of  the  cere- 
bellum to  the  cortex  on  the  opposite  side.  It  extends  vertically 
throughout  the  pons  and  is  continuous  with  the  arcuate  nucleus 
and  ponto-bulbar  nucleus  of  the  medulla.  The  nucleus  pontis 
receives  the  terminals  of  the  descending  tracts  which  form  the 
inner  and  outer  fifths  of  the  basis  pedunculi  and  the  inter- 


3o6 


THE  RHOMBENCEPHALON 


mediate  bundle  of  the  same,  and  thus  connects  these  tracts  with 
the  cerebellum.     It  forms  a  relay  in  the  indirect  efferent  path. 

The  cells  of  the  nucleus  pontis  are  all  emigrants  from  the  rhombic  lip  of 
the  myelencephalon.  Essick  has  traced  their  migration  during  the  latter 
half  of  the  second  and  all  the  third  and  fourth  months  (Am.  Jour.  Anat., 
Vol.  13).    This  is  a  superficial  migration.    It  proceeds  upward  to  the 


Fig.  115. — Transverse  section  through  superior  part  of  pons.  Weigert-Pal 
stain;  meduUated  fibers  are  black,  gray  substance  is  light. 

a.  Decussating  fibers  of  trochlear  nerve,  b.  Medial  longitudinal  bundle  and  anterior 
tecto-spinal  tract,  c.  Thalamo-olivary  tract,  d.  Brachium  conjunctivum.  e.  Field  of 
lateral  tecto-spinal,  thalamo-spinal,  rubro-spinal  and  lateral  reticulo-spinal  tracts,  f. 
Nucleus  pontis.  g.  Basilar  longitudinal  fibers,  h.  Dorsal  longitudinal  bundle  of  Schutz. 
i.  Mesencephalic  root  of  trigeminal  nerve,  j.  Spino-thalamic  track,  k.  Nucleus  of  lateral 
fillet.     1.  Medial  fillet,     m.  Basilar  transverse  fibers  of  pons. 


level  of  the  root  of  the  trigeminal  nerve;  there  it  bends  transversely  across 
the  pons,  marking  out  the  path  of  the  fasciculus  obliquus.  The  growing 
axones  push  the  cell-bodies  along  the  migrating  stream  to  their  destination 
in  the  opposite  nucleus  pontis.  Certain  cells  of  opposite  polarity  are  borne 
along  by  this  active  migration  a  variable  distance  toward  the  nucleus 
pontis;  others  remain  behind  in  the  rhombic  lip.  The  remaining  cells  of 
the  rhombic  lip  and  the  laggard  cells  that  become  fixed  along  the  stream  by 


OLIVARY   NUCLEI   OF   PONS 

the  increasing  firmness  of  the  neural  tissue,  constitute  the  nucleus  ponto- 
bulbaris  (corpus  ponto-bulbare)  described  by  Esseck  in  1907  (Anat.  Rec). 
The  migrating  stream,  0.2  mm.  wide,  flows  upward  between  the  facial 
and  intermediate  nerves,  where  the  ponto-bulbar  nucleus  is  found  in  the 
mature  brain.  Through  two  and  a  half  months  the  pontine  migration 
continues.  The  fibers  making  up  the  base  of  the  cerebral  peduncle  are 
descending  during  the  same  time,  hence  the  basilar  part  of  the  pons  is  built 
up  of  alternating  layers  of  longitudinal  and  transverse  fibers.  The  cells  of 
the  nucleus  pontis  give  origin  to  the  transverse  fibers,  while  those  of  the 
nucleus  ponto-bulbaris  originate  the  fibers  of  the  fascictdus  obliquus. 
Both  nuclei  receive  cerebro-pontal  fibers,  the  former  directly  from  the  base 
of  the  peduncle  and  the  latter  by  way  of  iht  fasciculus  circum-olivaris.  To- 
gether the  axones  of  both  nuclei  form  the  brachium  pontis. 

The  gray  matter  of  the  pars  dorsalis  includes  (i)  the  olivary 
group  of  nuclei,  viz.,  the  superior  olivary  nucleus,  the  nucleus 
of  the  corpus  trapezoideum,  the  preolivary  nucleus  and  the 
semilunar  nucleus;  (2)  the  nuclei  of  the  formatio  reticularis,  viz., 
the  nucleus  centralis  superior,  medius  and  inferior,  and  the 
nucleus  lateralis  medius;  and  (3)  the  nuclei  of  cerebral  nerves — • 
the  fifth,  sixth  and  seventh,  and  a  part  of  the  vestibular  nucleus 
of  the  eighth  nerve. 

I.  Olivary  Group. — The  superior  olivary  nucleus  (n.  olivaris 
superior)  is  situated  in  the  lateral  part  of  the  formatio  reticu- 
laris in  the  dorsal  portion  of  the  corpus  trapezoideum  (Fig.  114). 
It  lies  just  ventral  to  the  nucleus  of  the  facial  nerve  and  ventro- 
lateral to  the  olivary  bundle  of  fibers.  The  nucleus  contains 
small  bodied  nerve  cells;  and  in  this  respect,  resembles  the 
olive  of  the  medulla.  Its  outline  is  crescentic,  convex  toward 
the  median  line.  In  size  it  is  microscopic.  According  to 
Bruce  and  Cunningham  it  is  continuous  with  the  nucleus  of  the 
lateral  fillet.  The  superior  olive  constitutes  a  subordinate  relay 
in  the  auditory  path,  receiving  fibers  from  the  cochlear  nuclei 
of  both  sides  and  contributing  fibers  to  both  lateral  fillets 
(Fig.  119). 

The  superior  olivary  nucleus  gives  off  a  small  strand  of  fibers 
called  the  olivary  pedicle  which  runs  dorso-medially  between 
the  roots  of  the  facial  and  abducent  nerves,  to  the  nucleus  of  the 
abducent  nerve;  there  some  of  its  fibers  end,  the  remainder  join 


3o8 


THE   RHOMBENCEPHALON 


the  medial  longitudinal  bundle  and  run  to  the  trochlear  and 
oculomotor  nuclei.  The  pedicle  forms  part  of  an  auditory- 
ocular  reflex  arc. 

A  small  accessory  nucleus,  called  the  nucleus  prceolivaris,  is 
situated  just  a  little  ventral  to  the  superior  olivary  nucleus; 
and  a  second  one  embraces  the  convexity  of  the  nucleus  olivaris 


Fig.  ii6. — Section  of  pons  through  the  facial  colliculus.  Weigert-Pal  stain; 
medullated  fibers  are  black,  gray  substance  is  light. 

,  a.  Medial  longitudinal  fasciculus,  b.  Thalamo-olivary  fasciculus,  c.  Nucleus  of  spinal 
tract  of  trigeminal  nerve,  d.  Descending  fibers  of  vestibular  nerve.  _  e.  Restiform  body. 
f .  Spinal  tract  of  trigeminal  nerve,  g.  Transverse  fibers  of  pars  basilaris  pontis.  h.  Medial 
fillet  intersected  by  the  transverse  fibers  forming  trapezoid  body.  6.  Root  fibers  of  ab- 
ducent nerve,  i.  Pyramidal  tract,  j.  Abducent  nucleus,  under  genu  of  facial  nerye. 
k.  Facial  nucleus.  1.  Vestibular  nucleus,  m.  Root  of  vestibular  nerve,  n.  Superi9r 
olivary  nucleus,  m.  Root  of  vestibular  nerve,  n.  Superior  olivary  nucleus,  o.  Trapezoid 
body.     p.   Nucleus  pontis. 

superior,  lying  on  the  medial  side  of  it.  The  latter  is  the  nucleus 
semilunaris. 

Nucleus  of  the  Trapezoid  Body  {n.  corporis  trapezoidei) . — 
This  nucleus  is  deeply  imbedded  in  the  trapezoid  body  ventro- 
medial to  the  superior  olivary  nucleus  (Fig.  1 1 6) .  Its  cell-bodies 
are  scattered  and,  like  the  other  nuclei  of  the  olivary  group,  it 
forms  a  partial  relay  for  the  auditory  path.     This  nucleus  is 


NUCLEI   IN  PONS  309 

peculiar;  the  fibers  it  receives  terminate  in  the  form  of  cup- 
shaped  discs,  acustic  cups,  which  are  in  direct  contact  with  its 
cell-bodies  (Heald). 

2.  The  nuclei  of  the  reticular  formation  contained  in  the 
pons  are  the  n.  centralis  superior,  n.  centralis  medius,  n.  centralis 
inferior  and  n.  lateralis  medius.  All  are  microscopic.  They  are 
made  up  of  large  scattered  cell-bodies  whose  axones,  dividing  T- 
like,  are  both  ascending  and  descending  in  direction  (Tscher- 
mak) .  We  may  divide  these  axones  into  two  groups,  a  crossed 
and  an  uncrossed.  The  crossed  fibers  pierce  the  median  plane 
and  become  longitudinal  in  the  formatio  reticularis  near  the 
ventricular  gray  matter  and  lateral  to  the  root  of  the  abducent 
nerve.  At  that  point  they  bifurcate  and  one  branch  runs  up- 
ward and  the  other  downward.  The  descending  branches  of 
the  crossed  fibers  (lateral  reticulo-spinal  tract)  pass  through 
the  substantia  reticularis  grisea  of  the  medulla  and  the  lateral 
column  of  the  spinal  cord  throughout  its  length;  they  end  in  the 
gray  crescent  in  successive  segments  until  exhausted  near  the 
end  of  the  cord  (Tschermak,  Barker).  The  uncrossed  fibers 
from  the  reticular  nuclei  enter  the  medial  longitudinal  bundle 
of  the  same  side  and  there  branch  T-like.  The  descending 
branches  (anterior  reticulo-spinal  tract)  run  with  this  bundle 
into  the  anterior  column  of  the  spinal  cord,  through  which  some 
of  them  continue  to  the  end.  They  occupy  the  outer  side  of  the 
anterior  funiculus  and  end  in  succession  in  the  anterior  columna 
of  gray  matter  (Tschermak  and  Barker).  Just  what  is  the 
destination  of  the  ascending  branches  of  either  group  of  fibers 
has  not  been  determined.  J.  S.  Collier  suggests  that  these 
tracts  from  the  reticular  nuclei  should  be  called  the  crossed  and 
uncrossed  ponto-spinal  tracts  (Brain,  Vol.  24,  1901). 

3.  Nerve  Nuclei. — The  nuclei  of  the  trigeminal  nerve  (nuclei 
nervi  trigemini)  are  two  in  number.  The  genetic  or  motor 
nucleus  of  the  fifth  nerve  (n.  motorius)  in  the  pons  is  a  continua- 
tion of  the  mesencephahc  nucleus.  It  is  rather  close  to  the 
fourth  ventricle  in  the  extreme  lateral  part  of  its  floor,  under- 
neath the  locus  caeruleus  (Fig.  112).  It  extends  as  far  down  as 
the  middle  of  the  pons,  where  the  whole  group  of  axones  passes 


3IO 


THE   RHOMBENCEPHALON 


forward  into  the  motor  root  of  the  nerve.  The  dark  ferruginous 
cells  of  the  locus  caeruleus  form  no  part  of  the  motor  nucleus 
of  the  fifth  and  have  no  connection  with  either  of  its  roots 
(Horsley).  The  pontine  part  of  the  motor  nucleus  of  the 
trigeminal  nerve  is  purely  somatic,  in  that  it  suppHes  voluntary 


Fig.  1 17. — Diagrammatic  superior  section  of  pons.  Motor  fibers  and  descend- 
ing tracts  are  red,  sensory  fibers  and  ascending  tracts  are  blue,  gray  substance 
is  light. 

a.  Decussating  fibers  of  trochlear  nerve,  b.  Dorsal  longitudinal  bundle  of  Schutz.  c. 
Anterior  tecto-spinal  tract,  d.  Gustatory  tract,  e.  Spino-thalarnic  tract,  f.  Field  of 
lateral  tecto-spinal,  thalamo-spinal,  rubro-spinal  and  lateral  reticulo-spinal  tracts,  g. 
Medial  fillet,  h.  Deep  transverse  fibers  of  the  pars  basilaris.  i.  Superficial  transverse 
fibers  of  the  pars  basilaris.  j.  Medial  longitudinal  bundle,  k.  Mesencephalic  root  of 
trigeminal  nerve.  1.  Thalamo-olivary  tract,  m.  Brachium  conjunctivum.  n.  Lateral 
fillet,  o.  Basilar  longitudinal  fibers  from  the  base  of  cerebral  peduncle,  p.  Nucleus 
pontis. 

body  muscles  (soma-hody).  The  mesencephalic  nucleus  is 
commonly  considered  a  motor  nucleus  whose  axones  enter  into 
the  main  motor  root  of  the  fifth  (the  masticator  nerve) ;  but  its 
real  nature  is  much  in  doubt  (see  p.  239). 

Cortical  Connection. — The  nucleus  receives  motor  fibers  from 


SENSORY  NUCLEUS   OF   TRIGEMINAL  311 

the  opposite  pyramidal  tract  and  perhaps  from  the  cerebro- 
pontal  tracts  of  the  same  side;  and  sensory  fibers  terminate 
in  it  from  the  sensory  root  of  the  fifth  nerve,  and  from  the 
terminal  nuclei  of  other  common  sensory  nerves,  through  the 
medial  longitudinal  bundle  and  establish  its  rejkx  connections, 
Cerebello-tegmental  fibers  in  the  brachium  conjunctivum  also 
terminate  in  it;  and  the  vestibular  nuclei,  connected  with  the 
cerebellum  by  the  cerebello-tegmental  fibers  of  the  restiform 
body,  send  fibers  to  it,  all  of  which  bring  coordinated  reflex  im- 
pulses from  the  cerebellum. 

The  terminal  or  sensory  nucleus  {n.  terminalis  or  sensihilis) 
of  the  trigeminal  nerve  begins  at  the  middle  of  the  pons  and 
extends  to  the  second  segment  of  the  spinal  cord.  At  its 
superior  end  it  is  ventro-lateral  to  the  motor  nucleus  and  under 
cover  of  the  brachium  conjunctivum  of  the  cerebellum  (Figs. 
112  and  114).  Near  the  medulla  it  lies  ventro-medial  to  the  resti- 
form body  and  the  vestibular  root  of  the  acustic  nerve.  This 
part  of  it  is  almost  in  contact  with  the  nucleus  of  the  facial 
nerve  and  its  distance  from  the  ventricle  is  greater  than  it  is 
higher  up.  The  nucleus  is  gelatinous  in  character  and  is  con- 
tinuous with  the  same  substance  in  the  posterior  columna  of 
the  spinal  cord.  It  receives  the  sensory  root  of  the  trigeminal 
nerve.  Just  lateral  to  it  runs  the  spinal  tract  of  the  fifth  nerve, 
the  fibers  of  which  gradually  bend  into  the  nucleus  and  ter- 
minate in  rich  arborizations .  M ay  and  Horsley  traced  ascending 
rami  from  the  sensory  root  of  the  trigeminal  nerve  up  to  the 
level  of  the  middle  of  the  superior  quadrigeminal  colliculus  and 
they  inferred  from  this  fact  that  the  sensory  nucleus  of  the 
trigeminal  reaches  to  that  level.  But  those  ascending  rami  may 
be  purely  of  reflex  function,  the  arc  having  only  two  neurones. 
Axones  from  the  nucleus  pursue  several  different  courses:  (a) 
Reflex  fibers  go  directly  to  the  motor  nucleus  of  the  fifth  and 
through  the  medial  longitudinal  bundle  to  other  motor  nuclei. 
Coordinating  reflex  fibers  run  through  the  restiform  body  to  the 
cerebellar  cortex  and  are  connected  with  motor  nuclei  by  cortico- 
nuclear, cerebello-tegmental  and  vestibular  fibers,  {b)  ^Tactikt 
pain  and  temperature  fibers  are  supposed  to  enter  the  opposite 


312 


THE   RHOMBENCEPHALON 


spino-thalamic  tract  through  which  they  reach  the  thalamus; 
perhaps  some  run  through  the  ventral  spino-cerebellar  tract 
to  the  cerebellum,  (c)  Tactile  and  muscular  sense  fibers  pro- 
ceed to  the  thalamus,  probably  through  the  medial  fillet  on  the 
opposite  side. 


Fig.  ii8. — ^Diagrammatic  section  of  pons  near  its  lower  end.  Motor  fibers  and 
descending  tracts  are  red,  sensory  fibers  and  ascending  tracts  are  blue;  gray- 
matter  is  light. 

a.  Medial  longitudinal  fasciculus,  b.  Anterior  tecto-spinal  tract,  c.  Thalamo-olivary 
tract,  d.  Gustatory  tract,  e.  Nucleus  of  spinal  tract  of  trigeminal  nerve,  lying  medial  to 
the  tract,  f.  Lateral  vestibular  nucleus  (of  Deiters).  g.  Restiform  body.  h.  Superior 
olivary  nucleus  giving  off  olivary  pedicle,  i.  Root  of  vestibular  nerve,  j.  Transverse 
fibers  of  pars  basilaris  pontis.  6.  Root  fibers  of  abducent  nerve,  k.  Pyramidal  tract. 
I.  Dorsal  longitudinal  bundle  of  Scbutz.  m.  Nucleus  of  abducent  nerve,  and  genu  of  facial 
nerve  winding  over  it.  o.  Nucleus  of  facial  nerve,  p.  Medial  vestibular  nucleus  (of 
Schwalbe).  q.  Field  of  lateral  tecto-spinal,  thalamo-spinal,  rubro-spinal  and  lateral  retic- 
ulo-spinal  tracts,  r.  Trapezoid  body.  s.  Medial  fillet  intersecting  the  trapezoid  body. 
t.  Nucleus  pontis. 


Nucleus  of  the  Abducent  Nerve  (n.  nervi  abducentis). — This 
motor  nucleus  is  close  to  the  median  plane  and  is  separated 
from  the  ependyma  of  the  ventricular  floor  only  by  the  fibers 
of  the  seventh  or  facial  nerve.  It  is  situated  in  the  colliculus 
facialis  and  is  purely  somatic  (Figs.  112  and  114).     The  root- 


FACIAL   NUCLEUS 


3^3 


fibers  of  the  facial  nerve  run  lateral  to  the  sixth  nucleus,  de- 
scribe a  loop  on  its  dorsal  surface  and  then  return  lateral  to  it. 
Cortical  Connection. — The  abducent  nucleus  receives  the  end- 
tufts  of  motor  fibers  from  the  opposite  pyramidal  tract  and 
from  the  cerebro-pontal  tracts.  It  receives  reflex  impulses 
through  the  anterior  tecto-spinal  and  medial  longitudinal 
bundles  and  the  pedicle  of  the  superior  oHvary  nucleus  and 
perhaps  also  through  the  brachium  conjunctivum  from  the 
cerebellum.  The  axones  of  the  cell-bodies  in  the  abducent 
nucleus  run  in  two  directions :  The  greater  number  run  ventre* 
lateralward  and  emerge  at  the  lower  part  of  the  pons  as  ab- 
ducent nerve;  a  small  bundle  of  axones  runs  to  the  oculomotor 
nucleus  on  the  opposite  side  by  way  of  the  medial  longitudinal 
bundle.  The  former  innervates  the  lateral  rectus  muscle  of 
the  eye  on  the  same  side  as  the  nucleus;  the  latter  through  the 
third  nerve  innervates  the  medial  rectus  of  the  opposite  eye, 
though  that  muscle  receives  independent  fibers  from  the  third 
also. 

The  nucleus  of  the  facial  or  seventh  nerve  (n,  nervi  facialis) 
is  somatic  motor  (Fig.  114).  It  is  situated  deep  in  the  pons  in 
the  lateral  part  of  the  formatio  reticularis  beneath  the  superior 
fovea.  Medio-ventral  to  it  is  the  superior  olivary  nucleus 
and  the  substantia  gelatinosa  (Rolandi)  lies  dorso-lateral  to  it. 
The  nucleus  is  placed  midway  between  the  spinal  tract  of  the 
fifth  nerve  and  the  olivary  fasciculus.  The  facial  nucleus  is 
prolonged  upward  somewhat  in  the  pons  and  the  superior  part 
of  the  nucleus  gives  origin  to  the  fibers  that  supply  the  frontalis, 
procerus  and  corrugator  supercilii  (Harman). 

Cortical  Connections. — It  receives  voluntary  motor  impulses 
from  the  cerebral  cortex  of  the  opposite  hemisphere  via  the 
pyramidal  tract  and  probably  fibers  of  the  cerebro-pontal 
tracts  terminate  in  it.  These  establish  its  motor  connections. 
The  reflex  connections  of  the  facial  nucleus  are  established  by 
fibers  from  the  spinal  tract  of  the  trigeminal  nerve,  from  the 
trapezoid  body  (Cunningham),  and  from  the  medial  longitudinal 
bundle.  The  axones  of  the  cell-bodies  in  the  nucleus  facialis 
all  enter  the  root  of  the  facial  nerve.     By  its  direction  this  root 


314 


THE   RHOMBENCEPHALON 


is  divided  into  three  parts,  viz.,  two  distinct  parallel  parts 
joined  by  a  very  short  ascending  portion,  (i)  The  recurrent 
part,  the  pars  prima,  runs  dorso-medianward  to  the  colliculus 
facialis  passing  lateral  and  then  dorsal  to  the  lower  end  of  the 
abducent  nucleus;  (2)  it  then  ascends  about  one-fifth  of  an  inch 
(Cunningham)  between  the  ventricular  ependyma,  dorsally, 
and  the  abducent  nucleus  and  medial  longitudinal  bundle, 
ventrally,  and  this  part  is  called  the  genu  internum;  and  (3) 
the  pars  secunda,  bending  sharply  outward  over  the  nucleus  of 
the  sixth  nerve,  then  plunges  ventrally  through  the  pons;  this 


b  -■ 
c  - 

d  - 

f>^^^ 

e  - 

^^'' 

KVlffi^ 

,h 

FiGJI^^Q. — Diagram  of  a  transverse  section  through  the  junction  of  the 
medulla  and  pons  showing  the  roots  and  nuclei  of  the  eighth  cranial  nerve  and  the 
auditory  paths  in  the  pons.     (After  Morris's  Anatomy.) 

a.  Bechterew's  nucleus.  b.  Nuc.  of  descending  root.  c.  Restiform  body.  d.  Lat. 
cochlear  nucleus,  e.  Ventral  nucleus,  f.  Vestibular  nerve,  g.  Semicircular  canals,  h. 
Cochlear  nerve,  i.  Choclea.  j.  Dorso-lateral  nucleus  (Deitersi).  k.  Dorso-medial 
nucleus.  1.  Lateral  fillet,  m.  Superior  olivary  nucleus,  n.  Nucleus  of  trapezoid  body. 
o.  Trapezoid  body. 

emergent  part  of  the  root  runs  between  the  nuclei  of  the  facial 
and  trigeminal  nerves.  The  root  of  the  facial  nerve  is  joined 
at  the  genu  internum  by  fibers  from  the  medial  longitudinal 
bundle  which  rise  in  the  oculomotor  and  hypoglossal  nuclei 
and  supply  the  facial  muscles  above  the  orbit  and  the  orbicularis 
respectively. 

Nucleus  Salivarius. — Kohnstamm,  Yagita  and  others  have 
located  a  salivary  nucleus  in  the  dog's  brain,  and  Anthony 
Felling  has  found  it  in  the  human  brain  (Brain,  Vol.  36).  The 
nucleus  salivarius  is  an  elongated  nucleus  situated  chiefly  in  the 


CROSSED   PARALYSIS  315 

reticular  formation  of  the  medulla,  dorsal  to  the  inferior  olive 
but  extending  up  into  the  lower  sections  of  the  pons  where  it 
lies  medial  and  slightly  ventral  to  the  facial  nucleus.  It  is 
made  up  of  cells  with  scanty  cytoplasm  (autonomic  or  sympa- 
thetic cells).  Inasmuch  as  it  supplies  glands  and  smooth 
muscle,  it  is  a  visceral  nucleus.  Its  axones,  running  through  the 
intermediate  and  glossopharyngeal  nerves,  terminate  in  the 
spheno-palatine,  submaxillary  and  otic  gangha,  through  which 
they  innervate  the  cells  and  blood-vessels  of  the  salivary  and 
other  glands.  Like  other  visceral  nuclei  of  the  brain,  the 
salivary  nucleus  belongs  to  the  cranial  autonomic  or  sympa- 
thetic  system.  Its  cortical  connection  is  unknown.  It  is  as- 
sumed to  have  abundant  reflex  connections,  especially  with  the 
nerves  of  taste  and  smell. 

Vestibular  Nucleus  of  the  Auditory  Nerve  (n.  nervi  vestibu- 
laris) (Fig.  116). — This  nucleus  is  made  up  of  three  parts:  (i) 
The  chief  nucleus  (Schwalbe) ;  (2)  the  nucleus  of  the  descending 
root,  and  (3)  the  nucleus  of  Deiters,  which  is  lateral  in  position. 
The  superior  parts  of  Schwalbe's  and  of  Deiters's  nuclei  ex- 
tend into  the  pons  just  medial  to  the  restiform  body,  and  the 
nucleus  of  Deiters  is  prolonged  dor  sally  along  that  body  to- 
ward the  cerebellum.  This  dorsal  extension  of  Deiters's 
nucleus  is  called  Flechsig's  or  Bechterew's  nucleus.  We  shall 
recur  to  the  vestibular  nucleus  in  the  medulla  where  the  greater 
part  of  it  is  located. 

Lesions  in  the  pons  are  usually  attended  by  crossed  paralysis. 
The  paralysis  and  anaesthesia  of  parts  supplied  by  spinal  and 
by  bulbar  nerves  are  on  the  opposite  side,  but  the  fifth,  sixth 
and  seventh  cerebral  nerves  of  the  same  side  as  the  lesion 
are  apt  to  be  involved.  If  the  spino-thalamic  and  anterior 
spino-cerebellar  tracts  are  involved  and  not  the  medial  fillet, 
the  pain  and  temperature  sense  is  lost,  but  there  is  no  ataxia;  if 
the  medial  fillet  be  destroyed  and  not  the  spino-thalamic  and 
ventral  spino-cerebellar  tracts,  then  the  pain  and  temperature 
sense  is  intact,  but  the  muscular  sense  is  lost  on  the  opposite 
side  of  the  body.  The  tactile  sense  is  impaired  in  both  cases. 
A  lesion  of  the  trapezoid  body  produces  almost  total  deafness; 


3l6  THE  RHOMBENCEPHALON 

of  the  lateral  fillet,  slightly  impaired  hearing  on  the  same  side 
and  nearly  complete  deafness  in  the  opposite  ear.  Conjugate 
deviation  occurs  when  the  nucleus  of  the  sixth  nerve  is  affected 
and  strabismus  when  the  root  fibers  but  not  the  nucleus  are 
involved.  The  strabismus  is  external  if  the  lesion  be  irritative 
and  internal  if  the  root  fibers  are  destroyed.  Destructive 
lesion  in  the  nucleus  of  the  seventh  nerve  causes  complete 
facial  paralysis,  Bell's  palsy,  if  the  whole  nucleus  is  involved. 
Also,  complete  facial  paralysis  occurs  if  the  root-fibers  of  the 
facial  nerve  be  destroyed  in  the  pars  secunda  or  in  the  genu 
internum. 

Crossed  paralysis  {hemiplegia  alterans)  is  characteristic  of 
lesions  in  the  mid-brain  and  pons.  Here  the  pyramidal  tract 
is  uncrossed  to  motor  nuclei  at  lower  levels;  hence,  a  lesion,  de- 
stroying it  produces  paralysis  on  the  opposite  side  of  the  body 
below  the  lesion.  But  the  same  lesion  may  destroy  the  root 
of  the  third,  fifth,  sixth  or  seventh  nerve  in  its  course  to  the 
surface  of  the  brain  and  paralyze  the  ocular,  masticator  or 
facial  muscles  on  the  side  of  the  lesion. 

RHOMBENCEPHALON 

SECTION  m.    THE  MEDULLA  OBLONGATA 
(MYELENCEPHALON) 

Situation. — The  medulla  oblongata  is  the  distal  or  caudal 
part  of  the  brain  (Figs.  21  and  33).  It  may  be  regarded  as  the 
expanded  intracranial  portion  of  the  spinal  cord,  hence  the 
synonym  spinal  bulb.  It  occupies  the  basilar  groove  of  the 
occipital  bone,  posterior  to  the  pons;  and  is  continuous  with  the 
spinal  cord  below  the  foramen  magnum.  Dorsally  it  is  in  part 
concealed  in  the  valley  of  the  cerebellum.  The  vertebral 
arteries  wind  forward  around  it,  and  form  the  basilar  at  its 
junction  with  the  pons. 

Size. — The  medulla  is  about  2.5  cm.  (i  in.)  long  and  dorso- 
ventrally  is  12-15  mm.  thick.  Its  width  at  the  lower  end  is 
12  mm.  (J^  inch).  At  the  upper  extremity  it  measures  from 
2-2.5  cm.  (0.75-1  inch)  in  width  (Figs,  iii  and  112). 


DEVELOPMENT   OF   MEDULLA 


317 


Its  shape  resembles  an  inverted  frustrum  of  a  cone  flattened 
dorso-ventrally  at  the  base.  The  truncated  apex  of  the 
frustum,  which  is  nearly  circular  in  outline,  is  continuous  with 
the  spinal  cord  and  the  flattened  base  joins  the  pons.  On 
the  anterior  surface  a  transverse  ponto-medullary  groove 
marks  the  boundary  between  the  medulla  and  pons.  The 
medulla  is  a  bilateral  organ  composed  of  symmetrical  halves 
(Figs.  Ill  and  112).  In  the  interior  the  two  halves  are  united 
by  both  gray  and  white  matter  in  the  raphe  but  on  the  surface 
they  are  partially  separated  by  the  anterior  and  the  posterior 
median  fissures  (fissura  mediana  anterior  and  /.  m.  posterior). 


Fig.  120. — Section  of  embryonic  medulla.     Length  of  back,  9.1  mm. 

{Gordinier  and  Minot  after  His.) 

RL.  Rhomboid  lip.     Ts.  Tractus  solitarius.     X.  Vagus  nerve.     XII.  Hypoglossal  nerve. 

These  fissures  are  continued  through  the  spinal  cord,  but 
neither  extends  the  whole  length  of  the  medulla.  The  anterior 
median  fissure  is  interrupted  in  the  lower  part  of  the  medulla 
by  the  crossing  of  two  large  tracts  of  fibers,  forming  the  decus- 
sation of  the  pyramids;  while  only  through  the  lower  half  of 
the  medulla  does  the  posterior  median  fissure  extend. 

Origin. — The  medulla  oblongata  is  developed  from  the  myel- 
encephalonof  the  embryo  (Figs.  17  and  120).  The  myelen- 
cephalic  floor  and  walls  thicken  and  form  the  greater  part  of  the 
medulla.  Inferiorly,  the  roof  undergoes  some  thickening  but 
it  stretches  out  into  a  single  layer   of  epithelium  superiorly 


3i8 


THE  RHOMBENCEPHALON 


which  is  continuous  at  its  upper  end  with  the  inferior  medullary 
velum  of  the  cerebellum. 

Ventricle. — The  common  cavity  of  the  posterior  brain- vesicle 
persists  in  the  mature  brain  as  the  fourth  ventricle  (Figs.  i8, 
1 20  and  130) .  The  fourth  is,  therefore,  the  ventricle  of  the  adult 
rhombencephalon  (see  p.  263). 

SURFACES 

The  medulla  oblongata  presents  four  surfaces :  The  anterior, 
posterior  and  two  lateral,  separated  by  the  anterior  lateral  and 
posterior  lateral  grooves.  In  the  upper  medulla  the  surfaces 
are  clearly  defined,  but  they  become  less  distinct  as  they  de- 

sf 


IP  ^ 

\  Fig.  121. — Section  of  embryonic  medulla. 

scend  to  the  inferior  and  nearly  circular  extremity  (Figs,  in, 
112  and  124). 

The  anterior  lateral  sulcus  (s.  lateralis  anterior)  separates 
the  anterior  from  the  lateral  surface,  and  is  in  line  with  the  ex- 
its of  the  anterior  roots  of  the  spinal  nerves.  No  corresponding 
groove  exists  in  the  cord.  From  the  anterior  lateral  groove 
issue  the  roots  of  the  hypoglossal  nerve  and  the  anterior  root 
of  the  first  cervical  nerve.  The  abducent  (or  sixth)  nerve 
emerges  nearly  in  line  with  it  from  the  transverse  groove  be- 
tween the  pons  and  the  medulla  (Fig.  in). 

Posterior  Lateral  Sulcus  (s.  lateralis  posterior) . — The  posterior 
lateral  sulcus  of  the  medulla  separates  the  lateral  from  the 
posterior  surface  (Figs.  112  and  113).     It  descends  between  the 


ANTERIOR   SURFACE   OF  MEDULLA  319 

olive  and  the  restiform  body  and  is  continued  through  the 
spinal  cord.  Through  this  sulcus  into  the  cord  run  the  posterior 
roots  of  the  spinal  nerves  and  likewise  the  sensory  roots  of  the 
vagus  and  glossopharyngeal  nerves  run  through  it  into  the 
medulla;  while  the  motor  roots  of  the  ninth  and  tenth  and  the 
cerebral  root  of  the  eleventh  nerve  emerge  from  the  medulla 
through  the  posterior  lateral  sulcus.  The  roots  of  the  seventh, 
eighth  and  intermediate  nerves  are  found  at  the  superior  end  of 
the  sulcus  in  the  transverse  groove  between  the  medulla  and 
pons.  The  posterior  lateral  sulcus  is  not  parallel  with  the  axis 
of  the  medulla,  but  bends  outward  and  forward  as  it  ascends. 
Inferiorly  it  is  obliterated  for  a  short  distance  by  the  crossing 
of  the  dorsal  fasciculus  spino-cerebellaris  (direct  cerebellar  tract) 
form  the  lateral  to  the  posterior  surface. 

The  anterior  surface  {fades  anterior)  of  the  medulla,  bounded 
on  either  side  by  the  anterior  lateral  sulcus,  extends  from  the 
transverse  sulcus  below  the  pons  down  to  the  spinal  cord 
(Fig.  in).  It  is  made  up  of  symmetrical  halves  united  below 
by  the  decussation  of  the  lateral  (crossed)  pyramidal  ti:acts  but 
separated  above  by  the  anterior  median  fissure  which  termi- 
nates at  the  inferior  end  of  the  pons  in  a  blind  foramen  (foramen 
caecum  of  Vicq  d'Azyr).  On  either  side  of  the  median  fissure 
the  anterior  surface  presents  a  fusiform  eminence,  most  promi- 
nent near  the  pons,  called  the  pyramid.  The  pyramidal  tract, 
which  we  have  already  traced  through  the  internal  capsule, 
basis  pedunculi  and  pons,  forms  the  pyramid  of  the  medulla. 
In  the  lower  part  of  the  medulla  the  pyramid  divides  into  two 
tracts,  viz.,  the  lateral  (or  crossed)  pyramidal  tract  and  the 
anterior  (or  direct)  pyramidal  tract  the  former  comprising  about 
the  medial  four-fifths  and  the  anterior  pyramidal  tract  the  lateral 
one-fifth  of  the  pyramid.  Frequently  we  see  a  small  bundle  of 
fibers  (cerebropontal  fibers)  diverge  from  the  pyramid  near  its 
middle  and,  winding  backward  below  the  olive,  ascend  behind 
it  along  the  restiform  body  to  the  ponto-bulbar  nucleus.  That 
is  the  fasciculus  circum-olivaris.  It  is  not  aways  discernible,  as 
it  may  be  submerged.  Transverse  fibers,  called  the  anterior 
external  arcuate,  are  also  seen  crossing  the  pyramid  from  within 


320  THE   RHOMBENCEPHALON 

outward.  They  form  a  more  or  less  continuous  sheet  of  fibers, 
which  emerges  from  the  anterior  median  fissure  and  winds 
around  the  medulla  to  the  posterior  surface,  where  its  fibers 
enter  the  restiform  body.  The  anterior  surface  is  identical 
with  the  surface  of  the  two  anterior  columns  of  the  medulla. 

Lateral  Surface  (J acies  lateralis,  Figs.  107  and  iii). — There 
are  two  lateral  surfaces,  a  right  and  a  left.  Each  is  bounded  by 
the  anterior  lateral  and  the  posterior  lateral  sulcus  and  is 
inclosed  between  the  roots  of  the  hypoglossal  nerve,  ventrally, 
and  those  of  the  ninth,  tenth  and  the  cerebral  portion  of  the 
eleventh,  dorsally.  Lateral  surface  is  synonymous  with  the 
surface  of  the  lateral  column.  The  lateral  surface  is  formed 
above  by  the  olive,  below  by  the  tracts  of  the  lateral  column  and 
winding  backward  over  both  are  the  anterior  external  arcuate 
fibers. 

The  olive  (oliva)  is  an  elongated  eminence,  13  mm.  (J^^  in.) 
in  length,  situated  just  below  the  pons  (Fig.  in).  It  is  pro- 
duced by  the  inferior  olivary  nucleus  in  the  lateral  column  of  the 
medulla  and,  superficially,  is  composed  of  fibers  continuous  with 
the  fasciculus  proprius  of  the  lateral  column  in  the  spinal  cord 
(Fig.  124). 

Lateral  Column  {funiculus  lateralis,  Fig.  in). — It  is  made 
up  of  three  great  bundles  of  fibers  (Figs.  1 24,  125  and  1 26) :  The 
lateral  fasciculus  proprius,  which,  splitting  into  a  superficial  and 
a  deep  lamina,  incloses  the  inferior  olivary  nucleus;  the  vestibulo- 
spinal tract,  running  down  the  anterior  lateral  sulcus;  and  the 
ventral  spino-cerebellar  and  spino-thalamic  tract  which  runs  up 
the  posterior  lateral  groove.  At  the  junction  of  the  medulla 
with  the  spinal  cord  the  dorsal  spino-cerebellar  fasciculus  (direct 
cerebellar  tract)  passes  from  the  lateral  to  the  posterior  surface. 
The  anterior  external  arcuate  fibers,  running  from  the  anterior 
surface  backward  to  the  restiform  body,  may  be  so  numerous 
as  to  conceal  the  lateral  column  and  lower  part  of  the  olive. 

The  posterior  surface  {fades  posterior)  of  the  medulla  com- 
prises all  the  surface  inclosed  between  the  diverging  posterior 
lateral  sulci  (Fig.  112).  It  embraces  the  surfaces  of  the  two 
posterior  columns  of  the  medulla. 


POSTERIOR   SURFACE   OF   MEDULLA  321 

Inferiorly,  it  is  divided  into  lateral  halves  by  the  posterior 
median  fissure  and  presents  four  bundles  of  fibers  in  each  half 
(Figs.  122,  125  and  133).  From  the  fissure  outward  they  are  as 
follows :  The  funiculus  gracilis,  funiculus  cuneatus,  tractus  spi- 
nalis n.  trigemini,  and  the  dorsal  spino-cerehellar  fasciculus.  The 
funiculus  gracilis  (Fig.  133)  is  a  continuation  of  the  medial  tract 
of  the  posterior  column  of  the  spinal  cord,  and  the  funiculus 
cuneatus  is  in  direct  continuity  with  the  lateral  tract  in  the  same 
column  of  the  cord.  These  two  bundles  leave  the  surface  and 
end  in  the  nuclei  of  these  columns  in  the  medulla.  The  spinal 
tract  of  the  trigeminal  nerve  is  here  situated  on  the  surface; 
its  fibers  end  in  the  underlying  gelatinous  substance.  The 
dorsal  spino-cerebellar  fasciculus  (direct  cerebellar  tract)  is 
continued  up  from  the  lateral  column  of  the  spinal  cord.  Re- 
maining on  the  surface  it  runs  up  to  the  cerebellum  through  the 
restiform  body. 

Superiorly,  the  posterior  surface  on  either  side  is  formed  by  a 
large  rounded  band  of  fibers,  the  restiform  body  (Figs.  122  and 
133).  The  restiform  body  {corpus  restiforme)  is  continued  up- 
ward to  the  pons  and  then  bends  backward  into  the  corpus 
medullare  of  the  cerebellum  in  connection  with  which  it  has 
already  been  studied.  It  enters  the  corpus  medullare  just 
lateral  to  the  origin  of  the  brachium  conjunctivum  and  radi- 
ates through  the  medullary  laminae  to  the  cortex.  The  resti- 
form body  contains  the  following  tracts:  The  dorsal  spino- 
cerebellar fasciculus,  external  arcuate  fibers,  reticulo-cerebellar 
fasciculus  from  the  lateral  nucleus  of  the  medulla,  olivo-cere- 
bellar  fasciculus,  direct  sensory  cerebellar  fibers  from  the  roots 
of  the  trigeminal  and  vestibular  nerves,  and  nucleo-cerebellar 
fibers  from  terminal  nuclei  of  cranial  nerves — all  of  which  are 
ascending  in  direction;  and  the  fastigio-bulbar  part  of  the  cere- 
bello-tegmental  tract,  which  is  a  descending  tract  (see  p.  269 
for  description  of  restiform  body).  A  single  layer  of  flattened 
epithelial  cells  stretches  between  the  two  restiform  bodies 
and  roofs  over  the  inferior  part  of  the  fourth  ventricle.  That  is 
the  roof  epithelium.  It  is  continuous  with  the  inferior  medullary 
velum  of  the  cerebellum;  and,  as  it  forms  a  part  of  the  dorsal 
21 


322 


THE   RHOMBENCEPHALON 


boundary  or  roof  of  the  fourth  ventricle,  it  really  belongs  to  the 
cerebellum.  It  conceals  the  ventricular  surface  of  the  medulla. 
The  sKght  crest  marking  the  line  of  attachment  of  the  roof 
epithelium  to  the  medulla  is  called  the  tcenia  of  the  fourth 
ventricle. 

The  roof  epithelium  (Figs.  1 20  and  122)  seen  in  the  mid-dorsal 
surface  of  the  medulla,  is  of  triangular  shape;  its  base  is  attached 
to  the  inferior  medullary  velum  of  the  cerebellum;  its  apex, 


Inferior  quadrigeminal 

colliculus 

Fourth  nerve 


Superior  medullary 
velum 


Frenulum  veil 
Lateral  fillet 


Restiform  body 


Taenia 
Epithelial  roof  of 
fourth  ventricle 
Cuneate  tubercle 
Clava 
Tuberculum  cinereum 


Inferior  medullary 
velum 
Chonoid  plexus 

Median  aperture 
(Magendi) 


Fig.  122. — Roof  and  lateral  walls  of  fourth  ventricle,  and  its  chorioid 
plexuses.     (After  Morris's  Anatomy.) 


which  is  directed  downward,  terminates  at  the  obex  and  covers 
the  inferior  angle  of  the  fourth  ventricle;  and,  laterally,  it|is 
attached  to  the  clava,  the  cuneate  funiculus  and  the  restiform 
body.  The  line  of  attachment  to  the  restiform  body  runs 
first  obliquely  upward  and  outward  and  then  transversely 
outward  inferior  to  the  lateral  recess.  The  borders  of  the  epi- 
thelial lamina  become  thickened  by  the  addition  of  neuroglia 
and  are  in  continuity  with  the  ependyma  of  the  ventricle.  The 
thickened  apex  of  the  epithelial  lamina  is  called  the  obex. 


FLOOR  OF  FOURTH  VENTRICLE  323 

With  the  pia  mater  investing  it,  termed  the  chorioid  tela  of  the 
fourth  ventricle,  this  roof  epithelium  is  perforated  in  the  median 
line  near  the  obex  by  a  foramen,  the  median  aperture  (apertura 
mediana  ventriculi  quarti,  Magendii)  and  over  each  lateral 
recess  by  the  lateral  aperture  {apertura  lateralis  ventriculi  quarti 
of  Luschka) .  The  lateral  apertures  are  so  small  as  to  be  seen 
with  difficulty  but  the  median  aperture  measures  7  mm.  in 
width  and  5  mm.  in  length.  These  foramina  establish  com- 
munication between  the  subarachnoid  space  and  the  ventricle. 
On  either  side  of  the  median  line  there  is  a  longitudinal  in- 
vagination of  the  epithelial  lamina  into  the  ventricle  and  a 
similar  transverse  one  just  below  the  inferior  medullary  velum, 
both  of  which  are  occupied  by  a  vascular  fold  of  pia  mater. 
This  fold  constitutes  the  chorioid  plexus  of  the  fourth  ventricle 
{plexus  chorioideus  ventriculi  quarti).  If  the  roof  epithelium 
be  torn  away,  as  it  usually  is  with  the  pia,  a  rough  line  of  separa- 
tion is  seen  winding  over  the  restiform  body.  That  line  is  the 
tcsnia  of  the  fourth  ventricle.  Two  layers  of  ependyma  form  it. 
It  represents  the  attenuated  edge  of  the  rhombic  lip,  which  is  so 
fertile  in  the  embryonic  period. 

When  the  roof  epithelium  is  removed,  the  lower  triangle  of 
the  floor  of  the  fourth  ventricle  is  brought  into  view  (Figs.  112 
and  133).  Notice  the  median  longitudinal  furrow  bounded  by 
the  eminenticB  mediates,  which  form  the  calamus  scrip torius; 
then  the  little  fossa  in  the  sulcus  limitans,  called  the  fovea  in- 
ferior, situated  lateral  to  the  middle  of  the  pen,  and  the  ala 
cinerea  {trigonum  vagi),  whose  superior  angle  is  formed  by  the 
fovea  inferior;  and,  last,  the  large  lateral  area,  located  above 
the  ala  cinerea  lateral  to  the  eminentia  medialis  and  crossed 
by  the  nearly  transverse  medullary  strice.  This  region  is  called 
the  area  acustica. 

WHITE  MATTER  OF  MEDULLA 

The  medulla  is  made  up  of  white  and  gray  matter  which  to- 
gether bound  ventrally  and  laterally  the  inferior  part  of  the 
fourth  ventricle  and  surround  the  upper  extremity  of  the  central 
canal  which  is  continuous  with  that  of  the  spinal  cord. 


324  THE   RHOMBENCEPHALON 

For  the  most  part  the  white  matter  of  the  medulla  is  con- 
tinuous with  the  longitudinal  fibers  of  the  pons  and  restiform 
bodies  above  and  with  the  spinal  cord  below;  the  bulbar  roots 
of  the  eighth  to  the  twelfth  cerebral  nerves  and  many  de- 
cussating or  commissural  fibers  of  the  reticular  substance  are 
also  included  in  the  white  substance. 

Substantia  Reticularis. — Superficially,  the  white  matter  is 
collected  into  great  bundles  of  fibers,  such  as  the  pyramids, 
lateral  column  and  restiform  body;  but,  in  the  deep  parts  of 
the  medulla,  the  white  matter  enters  into  a  great  network 
called  the  substantia  reticularis,  which  has  gray  matter  in  its 
meshes  (Figs.  123  and  125).  It  is  continuous  above  with  the 
reticular  formation  of  the  pons  and  below  with  the  fasciculi 
proprii  of  the  spinal  cord.  The  substantia  reticularis  contains 
many  scattered  fibers,  processes  of  its  intrinsic  neurones,  which 
form  a  frequently  interrupted  and,  for  the  most  part,  a  crossed 
ascending  and  descending  tract.  Transverse  and  oblique 
fibers  are  likewise  numerous  in  the  reticular  substance.  They 
are  chiefly  the  arcuate  fibers.  The  distinct  tracts  of  longitudi- 
nal fibers  contained  in  it  will  be  noticed  later  (p.  327).  The  gray 
substance  of  the  substantia  reticularis  is  composed  of  th.^  nucleus 
lateralis  inferior,  the  eighth  to  the  twelfth  cerebral  nerve  nuclei 
and  the  inferior  olivary  nuclei. 

Raphe  (Figs.  123  and  125) . — The  raphe  is,  primarily,  a  sagittal 
lamina  of  neuroglia  derived  from  the  floor-plate  of  the  myelen- 
cephalon.  It  lies  in  the  median  plane  and  joins  the  lateral 
halves  of  the  medulla  together.  It  is  very  distinct  in  the 
superior  part  of  the  medulla.  Below  the  level  of  the  olive,  it 
is  entirely  obliterated  by  the  fillet  and  pyramidal  decussations, 
The  raphe  is  pierced  transversely  by  decussating  and  commis- 
sural fibers  and  is  traversed  dorso-ventralward  by  the  anterior 
external  arcuate  fibers. 

The  white  matter  of  the  medulla  is  divided  by  the  direction 
of  its  fibers  into  three  classes  or  systems:  (i)  Transverse 
fibers;  (2)  dorso-ventral  fibers;  and  (3)  longitudinal  fibers. 

I.  The  transverse  fibers  of  the  medulla  are  really  more  or 
less  oblique  in  direction  and  most  of  them  are  arched.     They 


CROSSING   FIBERS   OF   MEDULLA  325 

include  the  fibers  of  the  following:     (a)  The  pyramidal  de- 
cussation (decussatio  pyramidum)  with  the  decussating  fibers 
of  the  pyramidal  tract  to  motor  nuclei  of  the  medulla;  (b)  the 
fillet   decussation   (decussatio   lemniscorum)    and   decussating 
afferent  fibers  from  terminal  nuclei  of  the  medulla  to  the  fillets, 
spino-thalamic  tract  and  medial  longitudinal  bundle;  (c)  com- 
missural fibers  connecting  bulbar  nuclei;  (d)  anterior  external 
arcuate  fibers;  {e)  olivo-cerebellar  fibers,  and  (/)  a  few  reticulo- 
spinal fibers  from  the  lateral  nucleus  of  the  medulla.     The 
pyramidal  decussation  (Fig.  126)  is  located  in  the  lower  half  of 
the  medulla.     About  four-fifths  of  the  pyramid  crosses  over 
through   it   and  becomes  the  lateral  pyramidal  tract  of  the 
spinal  cord.     The  lower  level  of   the  pyramidal  decussation 
marks  the  boundary  between  medulla  and  cord.     The  medial 
fillet,  the  anterior  and  the  posterior  external  arcuate  fibers  all 
rise  in  the  nucleus  funiculi  graciUs  and  nucleus  funiculi  cuneati. 
The  two  former  run  forward  and  cross  over  in  the  middle  of  the 
medulla,  forming  the  fillet  decussation  {decussatio  lemniscorum) , 
after  which  they  separate  (Fig.  125).     The  medial  fillet  bends 
upward  and  ascends  between  the  inferior  olives,  hence  its  name 
in   the   medulla,   stratum  interolivare  lemnisci.     The   anterior 
external  arcuate  fibers,  continuing  their  ventral  direction,  issue 
from  the  anterior  median  fissure  and  anterior  surface  of  the 
medulla  (Fig.  1 24) ,  then  arch  backward  around  the  medulla  to 
the  restiform  body,  through  which  they  enter  the  cerebellum. 
The  arcuate  nucleus  makes  a  small  contribution  to  the  anterior 
external  arcuate  fibers  which  probably  belongs  to  the  cerebro- 
ponto-cerebellar  system.     The  posterior  external  arcuate  fibers 
run  through  the  restiform  body  to  the  cerebellum  without  de- 
cussating.    The  external  arcuate  fibers,  which  rise  with  the 
medial  fillet,   conduct  impulses  of   the  tactile  and  muscular 
senses.     The  olivo-cerebellar  tract  is  a  large  one  (Fig.  123).     It 
comprises  many  of  the  internal  arcuate  fibers  of  the  medulla. 
Its  origin  is  in  the  inferior  olive  of  the  medulla;  decussating  it 
pierces  the  opposite  olive  and  continues  through  the  restiform 
body  to  the  cerebellar  cortex  of  the  vermis,  being  reinforced 
by  a  few  fibers  from  the  olive  of  the  same  side.    The  tract 


326  THE   RHOMBENCEPHALON 

is  visible  to  the  naked  eye  as  it  enters  into  the  lateral  part  of  the 
restiform  body. 

2.  The  dorso -ventral  fibers  of  the  medulla  are  found  in  five 
situations :  (a)  In  the  median  raphe ;  (b)  in  either  half  of  the  me- 
dulla between  the  anterior  and  lateral  columns,  running  in  a 
linear  series  of  ten  or  twelve  fascicles  toward  the  anterior  lateral 
sulcus,  and  (c)  in  several  bundles  not  exactly  in  linear  series, 
which  run  inward  or  outward  through  the  posterior  lateral 
sulcus  between  the  lateral  and  posterior  columns  of  each 
side. 

(a)  The  dorso-ventral  fibers  of  the  raphe  are  the  anterior 
external  arcuate  fibers  (Fig.  123).  These  can  be  traced  to  the 
cortex  of  the  cerebellum  through  the  restiform  body.  Their 
origin  is  in  the  nuclei  funiculi  gracilis  and  funiculi  cuneati 
(Fig.  125).  As  they  wind  outward  over  the  surface  of  the 
medulla  they  are  augmented  by  the  axones  of  the  nucleus 
arcuatus  which  lies  on  the  surface  and  among  the  fibers  of 
the  pyramid. 

The  root-bundles  of  the  eighth  to  the  twelfth  cerebral  nerves 
constitute  the  remaining  groups  of  dorso-ventral  fibers.  By 
them  the  medulla  is  divided  into  areas. 

{b)  The  root-bundles  of  the  hypoglossal  nerve  (Fig.  1 24)  run  from 
the  ventricular  gray  matter,  near  the  median  line,  ventro- 
lateral ward  to  the  anterior  lateral  sulcus  where  they  emerge. 
Inclosing  between  them  and  the  raphe  the  anterior  column 
they  also  separate  it  from  the  lateral  column.  A  corresponding 
part  of  the  sheet  of  gelatinous  gray  substance  in  the  ventricular 
floor  is  included  with  each  column. 

(c)  The  vestibular  root  of  the  auditory  nerve,  the  roots  of  the 
glossopharyngeal  and  vagus  and  the  cerebral  root  of  the  accessory 
nerve  form  the  third  group  of  dorso-ventral  fibers  (Fig.  124). 

The  motor  fibers  of  the  ninth,  tenth  and  cerebral  part  of  the 
eleventh  nerves  take  their  origin  in  nuclei  of  the  medulla  and 
emerge  from  the  posterior  lateral  sulcus;  while  the  sensory  fibers 
of  the  vagus,  glossopharyngeal  and  vestibular  nerves  enter  that 
sulcus  from  without  and  run  through  the  medulla  to  their 
terminal  nuclei  in  the  ventricular  gray  matter.     These  nuclei 


LONGITUDINAL  FIBERS  327 

both  genetic  and  terminal,  are  located  lateral  to  the  hypoglossal 
nucleus.  The  nerve  roots  rising  or  terminating  in  them 
separate  the  lateral  from  the  posterior  column.  The  posterior 
column  comprises  everything  dorsal  to  the  above  roots  of  the 
eighth  to  eleventh  cerebral  nerves.  It  thus  includes  the  lateral 
gray  matter  in  the  floor  of  the  fourth  ventricle. 

3.  Longitudinal  Fibers.- — In  the  medulla,  the  longitudinal 
fibers  are  chiefly  continuations  of  the  same  in  the  pons  and  the 
restiform  bodies;  they  are  also  continuous  with  the  tracts  of  the 
spinal  cord.  They  can  be  best  located  by  reference  to  the  three 
columns  bounded  by  the  above  dorso-ventral  fibers,  namely, 
anterior,  lateral  and  posterior  columns,  which  are  distinctly 
outlined  in  the  upper  half  of  the  medulla  (Figs.  123  and  124). 

Longitudinal  Fibers  of  the  Anterior  Column.— The  anterior 
column  of  the  medulla  lies  between  the  raphe  and  the  roots  of 
the  hypoglossal  nerve,  and  between  the  anterior  surface  and 
the  floor  of  the  fourth  ventricle  (Figs.  123  and  124).  It  con- 
tains the  pyramid,  the  medial  fillet,  the  medial  longitudinal 
bundle,  the  anterior  tecto-spinal  tract,  the  substantia  reticularis 
alba  and  two  nuclei,  the  arcuate  nucleus  and  the  medial 
accessory  olivary  nucleus.  Excepting  that  part  forming  the 
lateral  pyramidal  tract  and  the  medial  fillet,  this  column  is 
continued  in  the  anterior  column  of  the  spinal  cord.  It  is 
naturally  divided  into  a  ventral  and  a  dorsal  part,  or  the  region 
of  the  pyramid  and  the  region  of  the  substantia  reticularis 
alba. 

The  pyramid  (pyramis)  with  the  arcuate  nucleus  imbedded  in 
it  and  the  arcuate  fibers  winding  over  it,  occupies  the  ventral 
portion  of  the  anterior  column  (Figs.  11 1  and  123).  It  is  the 
continuation  of  the  pyramidal  tract  and  is  composed  of  axones 
of  the  Betz  cells  in  the  anterior  central  gyrus  of  the  cerebrum. 
The  pyramidal  tract  diminishes  in  size  as  it  descends  through 
the  pons  and  medulla,  because  some  of  its  fibers  terminate  in 
ramifications  about  the  cells  of  cerebral  nerve  nuclei.  ^  In 
the  lower  part  of  the  medulla  the  pyramid  breaks  up  into 
the  anterior  (direct)  pyramidal  tract  (lo  per  cent,  of  the  pyra- 
mid), which  descends  along  the  anterior  median  fissure  in  the 


328 


THE    RHOMBENCEPHALON 


same  side  of  the  spinal  cord  and  the  lateral  (crossed)  pyramidal 
tract  (80  per  cent,  of  the  pyramid)  which  after  decussating 
with  its  fellow  through  the  anterior  median  fissure,  runs  down  in 
the  lateral  column  of  the  opposite  side  of  the  cord  (Fig.  126). 
The  fibers  of  the  anterior  tract  cross  in  succession  to  the  oppo- 


FiG.  123. — Section  of  medulla  oblongata  near  the  pons.     Unstained. 
{Original.) 

a.  Hypoglossal  nucleus,  b.  Vestibular  nucleus,  c.  Tractus  solitarius.  d.  Restiform 
body.  e.  Substantia  reticularis.  f.  Hilus  of  olivary  nucleus  containing  olivo-cerebellar 
fibers,  g.  Anterior  lateral  sulcus,  h.  Pyramid,  i.  Anterior  median  fissure,  j.  Anterior 
tecto-spinal  bundle,  k.  Medial  longitudinal  bundle.  1.  Nuc.  tractus  spinalis  n.  trigemini. 
m.  Tractus  spinalis  n.  trigemini.  n.  Lateral  cochlear  nucleus,  o.  Ventral  cochlear  nucleus. 
p.  Ventral  spino-cerebellar,  spino-thalamic,  and  rubro-spinal  tracts,  q.  Posterior  lateral 
sulcus,  r.  Medial  fillet,  interolivary  stratum,  s.  Anterior  external  arcuate  fibers,  t. 
Arcuate  nucleus. 

site  side  of  the  cord,  through  the  white  anterior  commissure 
and  there,  with  the  fibers  of  the  lateral  pyramidal  tract,  ter- 
minate in  fibrillar  end-tufts  about  the  cell-bodies  in  the  gray 
matter.  Thus  the  pyramid  forms  a  crossed  cerebral  tract  for 
motor  cerebral  and  spinal  nerves.  A  small  number  of  pyrami- 
dal fibers  (lo  per  cent.)  diverge  lateralward  from  the  pyramid 


MEDIAL   FILLET  329 

in  the  medulla  and  descend  in  the  lateral  funiculus  of  the 
cord  without  decussation.  They  account  for  the  weakness 
on  the  well  side,  and  for  slight  motion  on  the  paralyzed  side, 
which  are  commonly  observed  in  hemiplegia.  If,  as  E.  A. 
Schafer  claims,  the  fibers  of  the  pyramidal  tracts  end  in  the 
posterior  columna  of  gray  matter,  then  at  least  one  neurone 
intervenes  between  them  and  the  motor  neurones  of  the  spinal 
nerves;  but  without  doubt,  they  enter  into  either  direct  or 
indirect  relations  with  those  neurones. 

The  division  of  the  pyramidal  tract  into  the  anterior  and 
lateral  is  not  constant  in  man;  the  anterior  tract  is  absent  in 
about  15  per  cent,  of  human  cords.  This  is  of  interest  when  we 
recall  that  in  lower  animals  the  tract  is  undivided.  In  cats 
the  whole  pyramidal  tract  decussates  to  the  lateral  funiculus  of 
the  spinal  cord  while  in  moles  the  entire  tract  descends  the  an- 
terior funiculus  without  decussation  or  division.  The  pyramidal 
tract  decussates  without  division  to  the  opposite  posterior 
funiculus  of  the  spinal  cord  in  the  albino  rat,  guinea-pig,  mouse, 
red  squirrel  and  chipmunk  (Ranson:  Am.  Jour.  Anat,  Vol.  14, 
and  Simpson:    Jour.  Comp.  Neurol.,  Vol  24). 

The  dorsal  part  of  the  anterior  column  is  occupied  by  the 
substantia  reticularis  alba  (Figs.  123  and  124).  It  contains  the 
bodies  of  very  few  nerve  cells  and  is  of  a  light  color.  The 
medial  accessory  olivary  nucleus  is  imbedded  in  it  near  the 
pyramid  and  among  the  fibers  of  the  fillet  and  three  definite 
bundles  of  longitudinal  fibers  have  been  demonstrated  in  it, 
namely,  the  medial  fillet,  the  anterior  tecto-spinal  tract  and  the 
medial  longitudinal  bundle. 

Medial  Fillet  (lemniscus  medialis). — Just  dorsal  to  the 
pyramid  in  the  anterior  area  of  the  medulla  at  the  level  of  the 
olives  is  a  large  bundle  of  fibers  called  the  interolivary  stratum 
of  the  fillet  (Figs.  123  and  125).  Situated  between  the  inferior 
olivary  nuclei,  it  is  on  that  account  so  named.  Superiorly,  it  is 
continued  as  the  medial  fillet.  The  medial  fillet  rises  from  the 
nucleus  funiculi  gracilis  and  nucleus  funiculi  cuneati  of  the 
medulla  and  crosses  through  the  median  raphe  in  the  fillet 
decussation.      As  the  fillet  runs  brainward,  it  receives  fibers 


330  THE    RHOMBENCEPHALON 

from  the  terminal  nuclei  of  common  sensory  cerebral  nerves 
and  from  the  vestibular  nuclei.     Along  its  lateral  border  it  is 
accompanied  for  a  short  distance  in  the  pons  by  the  lateral  fillet. 
The  medial  fillet  is  composed  of  ascending  axones  from  the 
terminal  nuclei  of  spinal  and  cerebral  nerves.     It  carries  ordi- 
nary sensations  (tactile  and  muscular)  to  the  superior  quadri- 
geminal  colliculus  by  the  few  fibers  constituting  the  superior 
fillet,  and  to  the  thalamus  by  the  greater  part  of  the  medial  fillet. 
The    medial    longitudinal    bundle    {fasciculus    longitudinalis 
medialis)  (Figs.  123  and  126)  which  we  have  studied  in  the  mid- 
brain and  pons,  constitutes  a  very  distinct  strand  in  the  superior 
half  of  the  medulla,  but  below  the  level  of  the  olive  it  can  be 
identified  in  the  medulla  oblongata  only  by  a  study  of  its 
medullation  or  of  its  degeneration.     It  is  continuous  with  the 
anterior  fasciculus  proprius  of  the  spinal  cord.     Its  location  is 
next  the  median  raphe  and  the  ventricular  gray  substance, 
immediately  anterior  to  the  hypoglossal  nucleus,  in  the  upper 
medulla.     The  same  position  is  occupied  by  it  in  the  mid-brain 
and  pons.     It  is  here  in  the  medulla  that  the  hypoglossal  fibers 
are  supposed  to  enter  it  and  run  up  to  the  colliculus  facialis, 
where  they  join  the  facial  nerve  at  the  internal  genu.     At  the 
middle  of  the  medulla  the  decussation  of  the  fillet  pushes  this 
bundle  forward  and  somewhat  away  from  the  median  plane,  so 
that  it  runs  between   the  fillet  decussation  and  the  medial 
accessory  olivary  nucleus.     Below  the  level  of  the  fillet  decus- 
sation it  runs  between   the  decussatio  pyramidum  and  the 
isolated  head  of  the  anterior  columna  of  gray  substance.     Rising 
primarily  in  the  gray  matter  of  the  cord,  the  ascending  part 
of  the  medial  longitudinal  bundle  is  augmented  in  the  medulla 
and  pons  by  fibers  from  the  terminal  nuclei  of  sensory  cerebral 
nerves.     Most  of  its  ascending  fibers  cross  the  median  line  and 
terminate  in  the  motor  cerebral  nuclei  on  the  opposite  side; 
these  form  the  middle  links  in  many  reflex  arcs;  a  few  decus- 
sate in  the  posterior  commissure  and  end  in  the  thalamus.     The 
latter  are  sensory  conduction  fibers.     The  descending  part  of  the 
medial    longitudinal    bundle    is    the    anterior    reticulo-spinal 
fasciculus  (see  pp.  152,  235  and  301), 


REFLEX  TRACT 


331 


The  anterior  tectospinal  bundle  (Figs.  123  and  126)  descends 
as  a  distinct  strand  from  the  opposite  superior  colliculus  of  the 
corpora  quadrigemina  to  the  medulla;  there  it  approaches  and 
mingles  with  the  medial  longitudinal  bundle;  it  is  continued 


Fig.  124.— Section  of  the  medulla  oblongata  at  the  middle  of  olive. 
Unstained.  {Original.) 
a.  Nucleus  of  12th  n.  b.  Vestibular  nucleus,  c.  Tractus  solitarius.  d.  Nucleus  am- 
biguus.  e.  Tractus  spinalis  n.trigemim.  f.  Medial  accessory  olivary  nuclei.  8-.  ^ostenor 
lateral  sulcus,  h.  Ant.  external  arcuate  fibers,  i.  Fasciculus  P^opr^s.  J:  f^l^JJf^® 
nucleus,  k.  Anterior  tecto-spinal  bundle  in  substantia  reticularis  alba.  {:  Medial  long 
tudinal  bundle,  m.  Nucleus  alae  cinerea.  n.  Taenia  of  ,4th  ventricle,  o.  R?stiform  Doay. 
p  Gelatinous  substance,  q.  Substantia  reticularis  grisea  nucleus  ^f ^^^^^VJl  "?^°*^ 
Ventral  spinoK:erebellar, .  spin9-thalamic.  and  rubro-spinal  ^racts.s.  Dorsal  acc^^ 
olivary  nucleus,  t.  Inferior  olivary  nucleus,  u.  Pyramid,  v.  Medial  fillet,  interouvary 
stratum. 


along  the  fissural  surface  of  the  anterior  column  in  the  cord. 
Its  termination  is  in  the  central  gray  substance,  chiefly  the 
cilio-spinal  centers.  It  forms  the  middle  link  in  the  visual 
reflex  arc.  Its  bulbar  and  spinal  portions  constitute  chiefly 
the  pupillo-dilator  tract  (see  pp.  155,  233  and  303). 


332  THE   RHOMBENCEPHALON 

Longitudinal  Fibers  of  the  Lateral  Column. — The  contents 
of  the  lateral  column  (Figs.  123  and  124)  are  as  follows:  Super- 
ficially, the  lateral  fasciculus  proprius,  the  vestibulo-spinal,  and 
the  ventral  spino-cerebellar  tracts  and  the  spino-thalamic  tract. 
Deeply  lies  the  substantia  reticularis  grisea.  Within  it  close 
to  the  ventral  spino-cerebellar  fasciculus  descend  the  rubro- 
spinal, thalamo-spinal,  lateral  tecto-spinal  and  lateral  reticulo- 
spinal tracts  and  the  thalamo-olivary  fasciculus  runs  down 
along  the  dorsal  surface  of  the  inferior  olivary  nucleus  close  to 
the  hilus.  Imbedded  also  in  the  substantia  reticularis  are 
the  nucleus  ambiguus,  the  nucleus  lateralis  inferior  and  the 
dorsal  accessory  olivary  nucleus,  and  in  the  fasciculus  proprius  is 
the  main  inferior  olivary  nucleus.  The  gray  matter  of  the 
substantia  reticularis  grisea  is  a  part  of  the  disintegrated 
anterior  columna  of  the  cord  and,  unlike  that  of  the  anterior 
column,  it  contains  the  bodies  of  many  large  nerve  cells. 

Lateral  Fasciculus  Proprius  (Fasciculus  Lateralis  Pro- 
prius, Figs.  1 24  and  125) . — The  whole  lateral  column  of  the  spinal 
cord  except  the  lateral  pyramidal  and  dorsal  spino-cerebellar 
tracts  is  continued  into  the  lateral  column  of  the  medulla. 
Composed  of  ascending  and  descending  axones  which  j  are 
commissural  and  associative  for  different  segments  of  the 
spinal  cord,  the  lateral  fasciculus  proprius  of  the  medulla  runs 
in  part  beneath  and  in  part  superficial  to  the  inferior  olivary 
nucleus;  beyond  the  olive  it  is  continued  in  the  substantia 
reticularis  grisea  of  the  medulla  and  reticular  formation  of 
pons  and  mid-brain.  Among  the  fibers  of  the  lateral  fasciculus 
proprius  ventral  to  the  olive  is  the  spino-olivary  or  triangular 
tract  of  Helwig  and  dorsal  to  the  olive  the  thalamo-olivary 
bundle. 

The  vestibulo-spinal  tract  (fasciculus  vestibulo-spinalis)  (Fig. 
131)  rises  in  the  nucleus  of  Deiters.  The  vestibulo-spinal  fasc- 
iculus appears  at  the  anterior  lateral  sulcus  near  the  lower  end 
of  the  medulla  and  decends  along  the  surface  of  the  cord  just  be- 
hind the  anterior  roots  of  the  spinal  nerves.  It  terminates  in  the 
gray  cresent  of  the  cord  forming  an  efferent  link  in  the  vestibular 
arc  of  equilibrium  and,  because  the  nucleus  of  Deiters  receives 


PAIN  PATH  333 

the  fastigio-bulbar  tract  from  the  cerebellum,  it  also  forms  a 
segment  of  a  long  cerebellospinal  path  made  up  of  three  sets  of 
neurones— the  cortical  and  fastigial  of  the  cerebellum  and  the 
vestibular  of  the  medulla.  The  whole  path  is  concerned  with 
coordination. 

Ventral  Spine -cerebellar  and  Spino-thalamic  tract  {fasciculus 
spino-cerehellaris  ventralis)  (Figs.  123  and  126). — These  two  , 
tracts  are  combined  into  one  throughout  the  cord,  medulla  and 
pons.  Near  the  isthmus  the  former  turns  backward  around  the 
brachium  conjunctivum  and  through  the  superior  medullary 
velum  and  ends  in  the  cortex  of  the  superior  vermis  cerebelli 
while  the  spino-thalamic  tract  continues  in  the  original  direc- 
tion to  the  lateral  nucleus  of  the  thalamus.  The  common 
spino-encephalic  tract  made  up  of  these  two  bundles  takes  its 
origin  from  the  base  of  the  anterior  columna  and  center  of  the 
crescent  of  gray  matter,  chiefly  on  the  opposite  side  of  the 
spinal  cord  and  crossing  through  the  white  anterior  commissure 
it  ascends,  mingled  somewhat  with  the  fibers  of  the  above  de- 
scending vestibulo-spinal  tract,  along  the  lateral  surface  of  the 
cord  (Barker).  It  runs  beneath  the  posterior  lateral  groove  of 
the  medulla  and  through  the  formatio  reticularis  of  the  pons, 
to  the  point  of  division  near  the  isthmus  rhombencephali 
whence  the  two  divisions  proceed  to  their  cerebellar  and 
thalamic  terminations,  as  above  stated.  The  tract  is  probably 
reinforced  in  the  medulla  and  pons  by  the  addition  of  axones 
from  the  opposite  terminal  nuclei  of  common  sensory  cerebral 
nerves  and,  rising  primarily  in  relation  with  the  posterior  roots 
of  spinal  nerves,  it  thus  forms  a  crossed  path  for  common  sensa- 
tions, spinal  and  cerebral.  It  conducts  tactile,  pain  and 
temperature  impulses  (see  pp.  159  and  300). 

The  rubro-spinal  tract  is  the  crossed  descending  tract  of 
the  red  nucleus  (Figs.  123  and  126).  Running  dorso-lateral  to  the 
inferior  olive  in  the  medulla  it  mingles  with  the  fibers  of  the 
ventral  spino-cerebellar  tract.  It  is  continued  down  the  cord, 
in  the  lateral  column,  to  the  lateral  columna  and  center  of  the 
gray  crescent  as  far  as  the  first  lumbar  segment  (see  pp.  161, 
229  and  304). 


334 


THE   RHOMBENCEPHALON 


Closely  associated  with  the  rubro-spinal  tract  in  the  reticular 
substance  of  the  medulla  there  are  three  other  fasciculi  which 
can  be  identified  by  degeneration  and  myelinization.  They  are 
the  thalamo-spinal  fasciculis,  lateral  tecto-spinal  fasciculus 
and  lateral  reticulo -spinal  fasciculus,  described  on  pp.  155, 
235  and  303.  Ventro-medial  to  these  tracts  the  thalamo -olivary 
fasciculus  can  be  seen  skirting  the  dorsal  wall  of  the  olive  near 
its  medial  end  and  gradually  terminating  it. 

LongitudiQal  Fibers  of  the  Posterior  Columns. — Thelongi- 


Funiculus  gracilis  and  nucleus 
Funiculus  cuneatus  and  nucleus 
Tractus  spinalis  n. 

trigemini^and  nuc. 


Dorsal    spino- 
cebellar  tract 


Central  gray  substance 

i      Commissural  nucleus  between"solitary 

Central  canal  [tracts 


Ventral  spino- 
cerebellar 
spino- thalamic 
and  triangular  tracts 

Inferior  olivary  nucleus 


Medial  longitu- 
dinal bundles 

Ventral   spino- 
cerebellar, 
spino-thalamic 
and  rubro- 
spinal tracts 

Triangular 
tract  (Helwigi) 


Medial  accessory  olivary  nuc. 

Fig.  125 


Vestibulo- spinal  tract 
Medial  fillet 
Fillet  decussation 
Section  of  the  medulla  oblongata  at  the  fillet  decussation. 
Unstained.     (Original.) 


tudinal  fibers  of  the  posterior  column  form  many  bundles  and 
the  bundles  are  different  in  upper  and  lower  medulla.  The 
substantia  reticularis  is  small. 

The  lower  medulla  contains :  The  funiculus  gracilis,  funiculus 
cuneatus,  tractus  spinalis  nervi  trigemini  and  dorsal  spino- 
cerebellar tract,  named  from  the  posterior  median  fissure  out- 
ward (Figs.  125  and  133).  In  the  upper  medulla  are :  The 
restiform  body  and  the  spinal  tract  of  the  fifth  cerebral  nerve 
at  the  surface  and  the  tractus  solitarius  in  the  interior  (Figs. 
123,  124  and  133). 


MUSCLE-SENSE  PATHS  335 

The  funiculus  gracilis  is  the  superior  end  of  the  ascending 
postero-medial  column  (GolFs  column)  of  the  spinal  cord. 
Near  its  extremity  it  expands  and  forms  the  clava,  and  then 
tapers  off  and  disappears  along  the  side  of  the  fourth  ventricle. 
The  clava  is  due  to  the  nucleus  funiculi  gracilis,  in  which  the 
fibers  of  the  column  end.  The  funiculus  gracilis  is  composed  oi 
ascending  branches  of  the  posterior  roots  of  the  spinal  nerves 
which  enter  the  cord  below  the  seventh  or  eighth  thoracic 
segment. 

Funiculus  Cuneatus  (Figs.  125  and  133). — It  is  separated  from 
the  posterior  median  fissure  by  the  gracile  bundle  and  is  the 
continuation  of  the  ascending  postero-lateral  colum^n  (Burdach's 
column)  of  the  spinal  cord.  It  ends  about  the  cells  of  the 
nucleus  funiculi  cuneati  and  accessory  nucleus  funiculi  cuneati, 
which  form  the  cuneate  tubercle  seen  on  the  surface.  The 
fibers  of  the  funiculus  cuneatus  are  ascending  branches  of  the 
posterior  roots  of  the  spinal  nerves.  The  nerves  contributing 
to  this  column  are  the  cervical  and  the  six  or  eight  upper  thoracic. 
The  funiculi  gracilis  and  cuneatus  carry  to  the  nuclei  of  these 
columns  common  sensations  belonging  to  the  tactile  and 
muscular  senses.  Interference  with  these  tracts  produces 
ataxia. 

Spinal  Tract  of  the  Trigeminal  Nerve  {tractus  spinalis  nervi 
trigemini,  Figs.  123  and  133). — ^It  forms  a  narrow  strip  of  the 
posterior  surface  of  the  medulla  which  is  broadest  near  the 
restiform  body  and  tapers  downward  toward  the  spinal  cord. 
It  is  composed  of  the  descending  fibers  from  the  sensory  root 
of  the  trigeminal  nerve:  the  sensory  fibers  of  this  nerve  on  enter- 
ing the  pons  divide  T-like  into  an  ascending  and  a  descending 
branch  and  the  descending  branches  form  the  spinal  tract  of  the 
nerve,  which  for  a  short  distance  is  visible  on  the  surface  of  the 
medulla.  This  tract  is  continued  through  two  segments  in  the 
spinal  cord.  The  nucleus  of  the  spinal  tract  of  the  trigeminal 
nerve  over  which  it  runs  and  in  which  it  terminates  is  but 
the  continuation  of  the  gelatinous  substance  of  the  posterior 
columna  of  gray  matter  in  the  cord;  in  the  upper  medulla  it  is 
situated  ventro-medial  to  the  restiform  body.     The  nucleus 


S3^  THE   RHOMBENCEPHALON 

produces  a  slight  eminence  below  the  level  of  the  clava  called 
the  tuber culum  cinereum. 

The  dorsal  spino-cerebellar  fasciculus  of  Flechsig  {fasciculus 
spino-cerehellaris  dorsalis,  Figs.  131  and  132)  in  the  lower  medulla 
crosses  the  posterior  lateral  groove  and  the  spinal  tract  of  the 
fifth  nerve,  going  from  the  lateral  column  of  the  cord  to  the  pos- 
terior area  of  the  medulla;  it  then  ascends  to  form  a  consider- 
able part  of  the  restiform  body.  It  takes  its  origin  from  the 
nucleus  dorsalis  (Clarki)  in  the  spinal  cord.  It  ends,  very 
largely  on  the  opposite  side,  in  the  cortex  of  the  superior  cere- 
bellar worm.  The  dorsal  spino-cerebellar  fasciculus  is  a  vis- 
ceral afferent  tract  as  its  origin  in  the  visceral  terminal  nucleus 
of  the  spinal  cord  indicates.  It  is  concerned,  therefore,  with 
the  production  of  the  sympathetic  reflexes. 

Restiform  Body  (corpus  restiforme). — In  the  upper  medulla 
forming  the  lateral  part  of  each  posterior  area  is  a  large  rounded 
bundle  of  fibers  called  the  restiform  body  (Figs.  123, 124  and  133). 
It  is  the  largest  bundle  in  the  medulla  and  joins  it  to  the 
cerebellum.  The  restiform  body  may  be  divided  into  a  lateral 
and  a  medial  part.  The  lateral  part  contains  the  dorsal  spino- 
cerebellar fasciculus,  the  external  arcuate  fibers,  the  olivo-cere- 
bellar  fibers,  and  the  reticulo-cerebellar  bundle.  The  medial 
part  is  made  up  of  the  direct  sensory  cerebellar  fibers  from  nerve 
roots — especially  from  the  trigeminal  and  vestibular  nerves, 
the  nucleo-cerebellar  fibers  from  the  terminal  nuclei  of  the 
medulla,  and  the  fastigio-bulbar  bundle  of  the  cerebello- 
tegmental  tract.  The  last  tract  mentioned  is  a  descending 
tract,  all  others  of  the  restiform  body  are  ascending  tracts. 

The  restiform  body  is  inclosed  between  the  vestibular  and 
cochlear  roots  of  the  auditory  nerve  (eighth)  (Fig.  1 19) .  Ventral 
to  it  and  between  the  roots  is  the  ventral  part  of  the  cochlear 
nucleus ;  on  its  lateral  surface  and  among  the  fibers  of  the  lateral 
root  is  the  dorsal  or  lateral  part  of  the  same  nucleus.  The 
vestibular  nuclei — the  chief  dor  so-medial  nucleus  (Schwalbe), 
the  dorso-lateral  (Deiters),  the  superior  (Flechsig  and  Bechterew) 
and  the  nucleus  of  the  descending  root  are  situated  dorsal  and 
medial  to  the  restiform  body. 


PONTO-BULBAR   NUCLEUS 


The  restiform  body  is  partly  invested  by  the  corpus  ponto- 
bulbare  discovered  by  Essick.  The  ponto-bulbar  body  is  the 
tail  of  the  pontine  migration,  the  cells  that  lagged  behind  in  the 
formation  of  nucleus  pontis.  Its  position  is  revealed  by  the 
fasciculus  obliquus  which  originates  from  the  cell-bodies  of  the 
nucleus  ponto-hulharis.  The  ponto-bulbar  body  is  a  very  slender 
chain  of  neurones  extending  from  the  taenia  of  the  fourth  ven- 
tricle, caudal  to  the  acustic  tubercle,  obliquely  forward  between 


Funiculus  gracilis 
Funiculus  cuneatus 


Nucleus  funiculi  gracilis 

Nucleus  funiculi  cuneati 


Tractus  spinalis 

n.  trigemin 


Dorsal,  spino-cerebellar 
tract 


Vestibulo-spinal,  ventral  spino- 
cerebellar, spino-thalamic,  rubro 
spinal  and  triangular  tracts 


Nucleus  tractus  spinalis 
n.  trigemini 


'^Jr^  Head  of  ant.  columna 


\      Medial  longitudinal  and     pasciculus 
p  .,  \    anterior  tecto-spinal  oroorius 

Pyramid  \  bundles  J  P^°P""S 

Pyramidal  decussation 


Fig.  126. — Section  of  the  medulla  oblongata  at  the  pyramidal  decussation. 
Unstained.     {Original.) 


the  glossopharyngeal  and  acustic  nerves  and  then  upward 
between  the  facial  and  intermediate  nerves  into  the  pons. 
Having  crossed  the  ponto-meduUary  groove  it  continues  with 
the  fasciculus  obliquus  almost  to  the  root  of  the  trigeminal 
nerve.  Sometimes  the  inferior  extremity  of  the  body  is  a  thick 
*' tongue-shaped  mass"  visible  to  the  naked  eye;  more  often  it  is 
thinly  spread  over  the  restiform  body  and  is  visible  only  with 
the    microscope.     The    fasciculus    circum-olivaris    pyramidis 


33^  THE   RHOMBENCEPHALON 

terminates  in  the  nucleus  ponto-bulbaris  and  the  fasciculus 
ohliquus  pontis  originates  therein. 

Tractus  Solitarius  (Figs.  123  and  125). — The  sohtary  tract  is 
a  small  round  bundle  imbeded  in  the  lateral  part  of  the 
ventricular  gray  matter.  In  Weigert-Pal  sections  of  the  upper 
medulla  it  is  clearly  visible  to  the  naked  eye.  It  is  formed  by 
the  sensory  root  of  the  nervus  intermedins  and  the  ninth  and 
tenth  cerebral  nerves.  It  extends  through  the  nucleus  tractus 
solitarii  lateral  to  the  nucleus  of  the  ala  cinerea  and  slightly 
ventral  to  it  in  the  upper  medulla;  but,  trending  obliquely,  it 
descends  dorsal  to  that  nucleus  in  the  lower  medulla.  Gradu- 
ally approaching  the  median  plane,  the  two  solitary  tracts 
continue  through  the  central  gray  substance  of  the  lower  half 
of  the  medulla  to  its  end ;  Kolliker  claims  that  they  reach  to  the 
fourth  cervical  segment  but  his  findings  are  unconfirmed.  The 
solitary  tracts  meet  at  the  lower  end  of  the  medulla  in  the 
nucleus  commissuralis  of  Cajal.  In  man  the  solitary  tract  is 
made  up  largely,  if  not  wholly,  of  taste  fibers  from  the  inter- 
mediate and  glossopharyngeal  nerves.  The  nucleus  of  the 
tract  in  which  its  fibers  end  is  the  gustatory  nucleus  of  Nageotte 
whence  the  gustatory  tract  of  the  brain-stem  originates. 

The  solitary  tract  and  the  spinal  tract  of  the  trigeminal 
nerve  lie  on  the  surface  of  the  medulla  in  the  early  embryo, 
the  former  being  dorsal  to  the  other  and  close  to  the  rhombic 
lip.  They  are  alike  in  composition;  each  is  made  up  of  T- 
branched  root  fibers.  Later  both  are  submerged  by  the  thicken- 
ing of  the  rhombic  lip  and  the  development  of  the  restiform 
body.     Their  adult  position  is  thus  explained. 

GRAY  MATTER  OF  MEDULLA 

The  gray  matter  of  the  medulla  is  composed  (i)  of  that  con- 
tinuous with  the  nucleus  pontis,  called  the  arcuate  nucleus  and 
the  ponto-bulbar  nucleus;  (2)  of  the  sheet  of  gelatinous  gray 
substance  next  the  ventricle  and  the  nuclei  of  the  reticular 
substance  continuous  with  the  reticular  formation  and  ven- 
tricular gray  substance  of  the  pons;  and  (3)  of  special  nuclei  of 


OLIVO-ARCUATE    MIGRATION  339 

the  medulla,  viz.,  the  inferior  olivary  nuclei  and  the  nuclei  of 
the  funiculus  gracihs  and  funiculus  cuneatus. 

1.  Nucleus  Arcuatus  (Figs.  1 23  and  1 24).— The  arcuate  nucleus 
is  found  only  in  man.  It  forms  a  large  crescentic  mass  on 
the  ventral  and  medial  surface  of  the  pyramid.  Running 
over  and  through  it  there  are  the  anterior  external  arcuate 
fibers,  which  are  reinforced  by  a  small  tract  from  the  arcuate 
nucleus.  The  two  nuclei  are  sometimes  fused  across  the  median 
line  and  are  usually  continuous  with  the  nucleus  pontis.  The 
cells  of  the  arcuate  nucleus  are  large  and  stellate  like  those 
of  the  nucleus  pontis,  as  should  be  expected  because  of  their 
common  origin. 

They  are  emigrants  from  the  fertile  rhombic  lip  but  belong  to  a  dis- 
tinct migration  which  Essick  calls  the  olivo-arcuate  migration;  it  seems 
impossible  to  clearly  distinguish  the  migration  that  forms  the  arcuate 
nucleus  from  that  which  gives  rise  to  the  inferior  olivary  nuclei.  The  olivo- 
arcuate  migration  begins  early  in  the  second  month  in  a  20  mm.  embryo. 
At  first  it  is  intramedullary,  but  later  in  an  80  mm.  foetus  a  superficial 
migration  occurs  among  the  roots  of  the  vagus  nerve,  from  the  rhombic  lip 
to  the  anterior  surface  of  the  medulla.  The  stream  is  but  one  cell  deep  and 
two  or  three  cells  broad  at  first;- it  is  much  larger  in  the  96  mm.  foetus 
(about  three  months).  The  streams  flow  across  the  median  raphe  to  the 
region  of  the  opposite  pyramid  Hke  the  pontine  streams  and  intermingle 
with  each  other.  For  a  time  the  two  nuclei  remain  continuous;  but,  as 
the  migration  ceases  at  the  143  mm.  stage  (a  little  under  four  months)  and 
the  pyramidal  tracts  continue  to  enlarge  for  at  least  one  year  after  birth, 
the  nuclei  are  frequently  broken  apart  and  are  separate  in  the  adult.  The 
axones  of  the  arcuate  nuclei  reinforce  the  anterior  external  arcuate  fibers; 
they  run  chiefly  through  the  opposite  restiform  body  to  the  cortex  of  the 
vermis  cerebelli.  The  cerebral  relation  of  the  arcuate  nuclei  is  undeter- 
mined. According  to  Essick,  the  arcuate  nuclei  are  pecuHar  to  man  (Am. 
Jour.  Anat.,  Vol.  13). 

2.  The  gray  substance  in  the  substantia  reticularis  and  in 
the  immediate  floor  of  the  foiuth  ventricle  (Figs.  123  and  124) 
is  continuous  with  the  same  in  the  pons  and  mid-brain  above 
and  is  represented  in  the  spinal  cord  by  the  H-shaped  column 
of  gray  matter.  By  the  posterior  and  lateral  expansion  of  the 
neural  canal  in  the  upper  half  of  the  medulla  and  in  the  pons 
which  forms  the  fourth  ventricle  the  posterior  columnae  of  the 


340 


THE   RHOMBENCEPHALON 


H-shaped  column  of  gray  matter  are  pushed  outward  to  a  trans- 
verse direction  and  the  entire  bases  of  the  anterior  columnae  are 
brought  into  the  floor  of  the  ventricle.  The  expansion  of  the 
canal,  together  with  the  decussation  of  the  lateral  pyramidal 


Fig.    127. — Mid-olivary   section    of    the    medulla    oblongata;    Weigert-Pal 
stain;  white  substance  is  colored  black;  gray  matter  is  white. 

a.  Hypoglossal  nucleus,  b.  Nucleus  alae  cinereae.  c.  Solitary  tract  and  nucleus,  d. 
Restiform  body.  e.  Olivo-cerebellar  fibers,  f.  Hypoglossal  nerve  roots,  g.  Medial 
longitudinal  fasc.  and  anterior  tecto-spinal  tr.  h.  Dorsal  longitudinal  bundle  of  Schutz. 
i.  Medial  vestibular  nucleus  (of  Schwalbe).  j.  Lateral  vestibular  nucleus  (of  Deiters). 
k.' Dorsal  accessory  olivary  nucleus.  1.  Region  occupied  by  the  spino-cerebellar  and  spino- 
thalamic trs.  m.  Thalamo-olivary  tr.  n.  Inferior  olivary  nucleus,  o.  Pyramid,  p. 
Medial  accessory  olivary  nucleus. 


tracts  through  the  anterior  columnae  and  of  the  medial  fillets 
through  the  posterior  and  anterior  columnae,  disposes  the  H- 
shaped  column  as  follows: 

Anterior  Columna. — From  the  base  of  the  anterior  columna 


NUCLEI  341 

two  columns  of  cells  are  derived— a  lateral,  called  the  nucleus 
intercalatus  (of  Streeter)  and  a  medial  the  hypoglossal  nucleus 
(Figs.  123  and  124)  which  is  two-thirds  of  an  inch  in  length  and 
extends  along  the  median  raphe  in  the  upper  medulla  beneath 
the  eminentia  medialis.  It  is  continued  into  the  lower  medulla 
as  far  as  the  pyramidal  decussation.  By  commissural  fibers 
it  is  joined  to  the  nucleus  of  the  opposite  side  according  to 
KoUiker.  The  nucleus  is  purely  somatic:  its  cell-bodies  possess 
the  characteristic  somatic  structure  pointed  out  by  M alone, 
namely,  abundant,  tigrous  cytoplasm;  and  its  axones  supply 
only  striated,  voluntary  muscles  (Anat.  Rec,  Vol.  7).  It  gives 
origin  to  the  hypoglossal  nerve  proper  and  probably  to  a 
small  fasciculus  which  by  way  of  the  medial  longitudinal  bundle 
joins  the  facial  nerve  and  supplies  the  orbicularis  oris.  The 
hypoglossal  axones  run  in  linear  series  forward  through  the 
medulla  to  the  anterior  lateral  sulcus  whence  they  emerge  be- 
tween the  pyramid  and  the  olive  (Fig.  in).  They  separate 
the  anterior  from  the  lateral  column.  The  main  body  of 
the  anterior  columna  is  broken  up  into  the  nucleus  lateralis 
inferior,  the  nucleus  ambiguus  and  the  motor  part  of  the  nucleus 
of  the  ala  cinerea. 

The  nucleus  lateralis  inferior  (Figs.  123  and  125)  is  situated  in 
the  reticular  substance  of  the  lateral  column.  Though  it  is 
made  up  of  large  cell-bodies,  they  are  so  scattered  among  the 
fibers  of  this  region  that  the  nucleus  is  invisible  to  the  naked 
eye.  It  lies  subjacent  to  the  postero-lateral  sulcus,  medial  to 
Gowers'  tract  and  is  pierced  by  the  more  superficial  fibers  of 
the  olivo-cerebellar  fasciculus.  It  contributes  fibers  to  the 
anterior  and  lateral  reticulo-spinal  tracts,  which,  upon  enter- 
ing the  tract,  divide  T-like  and  furnish  both  ascending  and 
descending  fibers  to  them.  It  is  known  to  receive  fibers  from 
the  ventral  spino-cerebellar  tract  and  from  the  nuclei  funiculi 
gracilis  and  funiculi  cuneati  and  it  gives  rise  to  the  ascending 
tract  already  traced  to  the  cerebellum,  the  reticulo-cerebellar 
fasciculus,  which  probably  transmits  tactile,  muscular,  pain 
and  temperature  impressions  to  the  cerebellar  cortex. 

The  nucleus  ambiguus  (Fig.  124)  forms  an  irregular  sheet  of 


342  THE    RHOMBENCEPHALON 

gray  substance  which  extends  longitudinally  through  two- 
thirds  of  the  medulla.  It  lies  near  the  outer  limit  of  the  lateral 
column  dorso-medial  to  the  olivo-cerebellar  fasciculus.  It 
is  a  somatic  nucleus^  being  made  up  of  large  stellate  cell-bodies 
with  abundant,  tigrous  cytoplasm.  Its  axones  furnish  all  the 
voluntary  motor  fibers  of  the  glossopharyngeal  and  vagus  nerves 
and  make  up  the  entire  bulbar  root  of  the  accessory  nerve. 
They  emerge  from  the  posterior  lateral  sulcus  of  the  medulla, 
those  of  the  glossopharyngeal  and  vagus  between  the  res- 
tiform  body  and  the  olive,  the  accessory  fibers  emerge  below 
the  level  of  the  olive. 

The  nucleus  of  the  ala  cinerea  (Fig.  124)  is  in  part  derived  from 
the  base  of  the  anterior  columna;  this  part  is  efferent  in  func- 
tion and  its  neurones  resemble  those  of  the  lateral  columna  in 
the  cord.  It  belongs  to  the  tenth  nerve.  It  is  situated  above 
close  to  the  ependyma  of  the  fourth  ventricle  under  the  ala 
cinerea  and  it  extends  inf eriorly  into  the  closed  medulla  nearly 
as  far  as  the  hypoglossal  nucleus.  Because  of  its  relation  to 
the  nucleus  ambiguus  it  is  also  called  the  dorsal  nucleus  of  the 
vagus.  It  is  a  visceral  nucleus,  belonging  to  the  cranial  autonomic 
(or  sympathetic)  system.  Molhant  discovered  that  all  vagus 
fibers  supplying  smooth  and  heart  muscle  arise  in  the  dorsal 
nucleus  of  the  vagus,  the  nucleus  of  the  ala  cinerea.  In 
harmony  with  the  principle  of  differentiation  according  to  func- 
tion, the  nucleus  should  contain  two  varieties  of  cells — one  for 
smooth  muscle  and  the  other  for  striated  involuntary  (heart) 
muscle.  This  is  found  to  be  the  case.  In  the  central  nervous 
system  Malone  describes  three  varieties  of  efferent  neurones: 
the  somatic,  which  supply  voluntary  striated  muscle;  the  cardiac 
visceral,  which  innervate  involuntary  striated  muscle  (heart); 
and  the  common  visceral,  which  innervate  smooth  muscle 
(and  glands,  probably).  Both  kinds  of  visceral  neurones  are 
found  in  the  nucleus  of  the  ala  cinerea.  The  nucleus  is  com- 
posed of  three  parts :  the  superior  and  inferior  parts  are  common 
visceral  and  innervate  the  smooth  muscle  of  the  respiratory 
tract  and  of  the  alimentary  tract  down  to  the  left  colic  flexure; 
the  middle  part  is  the  nucleus  cardiacus,  the  inhibitory  nucleus 


NUCLEUS   CARDIACUS 


343 


of  the  heart.  The  cell-bodies  of  the  nucleus  cardiacus  possess 
a  medium  amount  of  the  tigrous  cytoplasm  occupying  an  inter- 
mediate position  between  the  somatic  and  the  common  visceral 
neurones  (Am.  Jour.  Anat.,  Vol.  1 5) .     All  efferent  visceral  nuclei 


Fig.  128. — Mid-olivary  section  of  medulla,  diagrammatic    Descending  tracts 

colored  red;  ascending  tracts  blue.. 
a.  Anterior  tecto-spinal  tr.  b.  Hypoglossal  nucleus,  c.  Dorsal  longitudinal  bundle  of 
Schutz.  d.  Nucleus  alae  cinereae.  e.  Solitary  tract  and  nucleus,  f.  Lateral  vestibular 
nucleus  (of  Deiters).  g.  Restiform  body.  h.  Nucleus  of  spinal  tract  of  the  trigeminal 
nerve  and  the  tract,  i.  Dorsal  spino-cerebellar  tr.  lo.  Vagus  nerve,  j.  Ventral  spino- 
cerebellar and  spino-thalamic  tracts,  k.  Field  occupied  by  rubro-spinal,  thalamo-spinal  and 
lateral  tecto-spmal  and  reticulo-spinal  tracts.  1.  Thalamo-olivary  tract.  12.  Hypoglossal 
nerve,  m.  Pyramid,  n.  Medial  fillet,  o.  Medial  longitudinal  bundle,  p.  Substantia  ret- 
icularis, q.  Nucleus  ambiguus.  r.  Medial  vestibular  nucleus  (of  Schwalbe).  s.  Lateral 
vestibular  nucleus  (of  Deiters).  t.  Arcuate  fibers  entering  restiform  body.  u.  Spinal  tract 
of  the  trigeminal  nerve,  v.  Dorsal  spino-cerebellar  tr.  w.  Anterior  external  arcuate  fibers. 
X.   Medial  accessory  olivary  nucleus. 


send  their  axones  out  to  sympathetic  ganglia  through  which  the 
actual  involuntary  muscles  and  glands  are  supplied.  From 
the  nucleus  of  the  ala  cinerea  the  axones  run  in  a  curve  convex 
toward  the  median  plane  between  the  restiform  body  and  the 


344  THE   RHOMBENCEPHALON 

olive.  They  are  joined  medially  by  those  axones  of  the  nucleus 
ambiguus  which  enter  the  roots  of  the  tenth  nerve.  By  this 
nucleus  and  the  nucleus  ambiguus  many  distinct  fascicles  are 
formed,  belonging  to  the  roots  of  the  ninth,  tenth  and  the  cere- 
bral part  of  the  eleventh  nerves.  They  run  in  slightly  different 
planes  but  all  of  them  emerge  in  the  region  of  the  posterior 
lateral  sulcus  of  the  medulla  (Fig.  in).  Intermingled  with 
the  motor  cells  of  the  nucleus  alae  cinereae,  there  are  the  small 
spindle  cells  of  the  terminal  nucleus  of  the  vagus  and 
glossopharyngeal  nerves  which  represent  neurones  of  the  pos- 
terior colun^na  of  gray  matter.  They  receive  the  end-tufts  of 
the  sensory  root  fibers  of  the  vagus  nerve  and  possibly  of  a 
small  number  from  the  glossopharyngeal  nerve. 

The  hypoglossal  nucleus  and  the  nucleus  ambiguus  receive 
many  fibers  from  the  opposite  pyramidal  tract  and  probably 
from  the  cerebropontal  tracts  which  bring  to  them  voluntary 
motor  and  inhibitory  impulses  from  the  cerebral  cortex;  their 
reflex  connection  is  established  (i)  by  fibers  of  the  medial  longi- 
tudinal bundle  which  rise  in  sensory  nuclei,  and  (2)  by  cere- 
bello- tegmental  fibers  of  the  brachium  conjunctivum  and  corpus 
restiforme,  the  latter  being  assisted  by  axones  of  the  nucleus  of 
Deiters. 

Nucleus  Salivarius: — The  salivary  nucleus  of  Kohnstamm, 
mentioned  in  the  description  of  the  pons,  is  present  almost 
wholly  in  the  medulla.  It  is  situated  in  the  reticular  substance 
of  the  lateral  column,  dorsal  to  the  inferior  olive.  The  lower 
part  of  this  nucleus  probably  contributes  the  secretory  and 
vasodilator  fibers  of  the  glossopharyngeal  nerve,  though  it  is 
possible  that  all  the  axones  of  the  salivary  nucleus  enter  the 
intermediate  nerve  (glosso-palatine  nerve),  as  is  suggested  by 
Hardesty;  they  all  terminate  in  sympathetic  ganglia,  especially 
in  the  spheno-palatine,  otic  and  submaxillary  and  in  smaller 
ganglia,  as  the  subhngual,  the  parotid  (of  Schochet),  etc. 

The  posterior  columna  is  decapitated  by  the  fillet.  It  is  repre- 
sented in  the  medulla  (i)  by  the  following  terminal  nuclei,  viz., 
the  sensory  part  of  the  nucleus  alae  cinereae  of  the  vagus  and 
glossopharyngeal  nerves,  the  vestibular  and  cochlear  nuclei  of 


A  VISCERAL   NUCLEUS  345 

the  auditory  nerve,  the  nucleus  tractus  solitarii  and  the  nucleus 
of  the  spinal  tract  of  the  trigeminal  nerve;  and  (2)  by  the  gray 
matter  of  the  reticular  substance  of  the  posterior  column.  All 
the  posterior  columna,  except  the  dorsal  nucleus  of  Clark,  form 
somatic  terminal  nuclei  (the  trigeminal,  vestibular  and  cochlear) ; 
the  dorsal  nucleus  of  Clark  forms  visceral  terminal  nuclei  (the 
afferent  part  of  the  nucleus  alae  cinereae  and  the  nucleus  tractus 
solitarii) . 

The  nucleus  alee  cinerece  of  the  vagus  and  glossopharyngeal 
nerves  (Fig.  124)  contains  in  its  lateral  part  a  group  of  small 
fusiform  cell-bodies  like  those  in  the  posterior  columna.  These 
fusiform  cells  constitute  the  terminal  nucleus  of  the  sensory 
fibers  of  the  vagUs,  and  it  is  probable  that  a  few  glossopharyn- 
geal fibers  also  arborize  and  end  in  the  nucleus.  This  is  a  visceral 
or  splanchnic  terminal  nucleus.  Cortical  Connection. — Axones 
of  this  nucleus  probably  enter  into  the  medial  fillet,  the  spino- 
thalamic tract,  the  restiform  body  and  the  medial  longitudinal 
bundle.  The  two  former  conduct  tactile,  muscular,  pain  and 
temperature  impulses  to  the  thalamus,  whence  the  cortical 
fillet  carries  them  to  the  cortex;  the  latter  establish  its  simple 
reflex  connection^  and,  by  way  of  the  cerebellum  and  cerebello- 
tegmental  tracts,  coordinated  reflex  connections.  The  intra- 
nuncial  connections  are  especially  rich. 

Nucleus  Tractus  Solitarii  (Figs.  123  and  125). — The  nucleus  of 
the  solitary  tract  surrounds  the  tractus  solitarius  with  which 
it  coincides  in  extent.  It  is  a  special  sense  visceral  nucleus, 
the  gustatory  nucleus  of  Nageotte.  It  is  a  part  of  the  central 
gelatinous  gray  substance  and  is  situated  just  lateral  to  the 
nucleus  of  the  ala  cinerea.  In  its  descent  it  trends  dorsally 
and  toward  the  median  line.  It  is  joined  to  the  opposite 
nucleus  at  its  spinal  end  by  the  nucleus  commissuralis  (Cajal). 
The  nucleus  of  the  solitary  tract  is  the  terminal  nucleus  of  the 
afferent  fibers  of  the  intermediate  and  glossopharyngeal  nerves 
and  probably  receives  a  few  fibers  from  the  vagus.  It  is 
thus  the  nucleus  of  the  nerves  of  taste  and  forms  the  first  relay 
station  in  the  gustatory  path.  The  axones  of  the  cell-bodies  in 
the  nucleus  ttactus  solitarii  establish  reflex  connections  with 


346 


THE   RHOMBENCEPHALON 


efferent    nuclei    and    continue    the    taste    path    toward    the 
thalamus. 

Nucleus  Tr actus  Spinalis  Nervi  Trigemini  (Figs.  123  and  126). 
— The  nucleus  of  the  spinal  tract  of  the  trigeminal  nerve  is 
gelatinous  in  character.  It  is  continuous  with  the  sensory  pon- 
tine nucleus  of  the  trigeminal  nerve  above  and  below  is  con- 


FiG.  129. — Section  of  the  medulla  at  the  fillet  decussation,  Weigert-Pal  stain; 

medullated  fibers  stained  black;  gray  substance  remains  light. 
a.  Nucleus  gracilis,  b.  Nucleus  cuneatus.     c.  Nucleus  of  the  spinal  tract  of  the  trigeminal 
nerve,     d.  Large   field  of    medullated    fibers,     e.  Medial   accessory   olivary   nucleus.^   f. 
Pyramid,     g. . Fillet  decussation,     h.  Funiculus  gracilis,     i.  Funiculus  cuneatus.     j.  Spinal 
tract  of  the  trigeminal  nerve,     k.  End  of  the  inferior  olivary  nucleus. 


tinned  in  the  gelatinous  substance  of  the  posterior  columna  of 
the  spinal  cord.  As  low  down  as  the  second  cervical  segment 
it  receives  fibers  from  the  trigeminal  nerve  so  the  terminal 
nucleus  of  this  nerve  extends  from  the  middle  of  the  pons  to  the 
second  cervical  nerve.  It  is  a  somatic  terminal  nucleus.  The 
nucleus  of  the  trigeminal  is  embraced  between  the  emergent 


CORTICAL   AND    REFLEX   CONNECTIONS  347 

part  of  the  facial  nerve  medially  and  the  vestibular  nerve 
laterally  in  the  lower  portion  of  the  pons;  in  the  upper  medulla 
the  nucleus  lies  along  the  ventro-medial  surface  of  the  restiform 
body;  it  enlarges  in  bulk  and  approaches  the  surface  near  the 
middle  of  the  medulla  where  it  produces  the  tuberculum  ciner- 
eum  and  it  is  then  continued  down  into  the  cord  as  a  cap  of 
the  posterior  columna  of  gray  substance.  In  the  lower  part  of 
the  medulla  the  nucleus  underlies  the  visible  part  of  the  tractus 
.spinalis  nervi  trigemini. 

The  sensory  root  of  the  trigeminal  nerve  (fifth)  enters  the  pons 
on  its  ventral  surface  in  line  with  the  roots  of  the  seventh, 
eighth,  ninth,  tenth  and  accessory  nerves  (Fig.  in).  The  root 
fibers  divide  T-like;  the  short  ascending  branches  end  in  the 
pontine  and  mesencephalic  nuclei  of  the  fifth  nerve  and  the 
long  descending  branches,  forming  the  spinal  tract,  terminate 
in  the  nucleus  of  that  tract.  A  certain  few  of  these  root- 
fibers  go  directly  to  the  motor  nucleus  of  the  trigeminal  nerve 
and  perhaps  to  other  motor  nuclei;  these  are  reflex  in  function. 

From  the  trigeminal  nucleus axones  establishing  reflex  dindcor- 
tical  relations  run:  {a)  To  motor  nuclei  by  way  of  the  medial 
longitudinal  bundle  and  directly  without  entering  that  bundle, 
forming  the  middle  link  of  simple  reflex  arcs,  and,  reinforced 
by  direct  root  fibers,  to  the  cerebellar  cortex  by  way  of  the 
restiform  body,  whence  the  coordinated  reflex  arcs  are  completed 
by  the  Purkinje,  cerebello-tegmental  and  Deiters's  neurones, 
or  by  the  two  former  and  those  of  the  red  nucleus  or  thalamus. 
{h)  By  way  of  two  paths  they  run  toward  the  cerebral  cortex 
as  far  as  the  thalamus.  The  latter  cross  the  median  raphe  and 
probably  enter  the  medial  fillet  and  the  spino- thalamic  tract. 
The  axones  bearing  impulses  of  the  muscular  sense  enter  the 
medial  fillet  and  are  continued  through  it  to  the  lateral  nucleus 
of  the  thalamus;  those  fibers  which  conduct  pain  and  tem- 
perature impressions  run  through  the  spino- thalamic  tract 
to  the  same  nucleus.  Both  sets  of  fibers  also  conduct  tactile 
impulses.  The  medial  fillet  conducts  impulses  leading  to 
tactile  discrimination  of  two  or  more  simultaneous  contacts 
and  the  spino-thalamic  tract  carries  impulses  of  tactile  locali- 


348  THE   RHOMBENCEPHALON 

zation  of  a  single  contact.  From  the  thalamus  the  cortical  fillet 
completes  the  path  to  the  somaesthetic  cortex  of  the  cerebrum. 
Vestibular  Nuclei  {nn.  nervi  vestibularis j  Figs.  123  and  124). — 
These  are  located  partly  in  the  pons  as  already  pointed  out,  and 
extend  as  low  as  the  mid-medulla.  They  are  somatic  terminal 
nuclei.  Their  function  is  equilibrium.  The  principal  nucleus 
(Schwalbe's)  is  dorso-medial  in  position  and  lies  beneath  the 
acustic  area  of  the  ventricular  floor,  crossed  by  the  medullary 
striae.  It  extends  transversely  from  near  the  eminentia  medialis 
almost  to  the  restiform  body.  It  appears  to  receive  nearly  all 
the  fibers  of  the  vestibular  nerve  which  arborize  and  terminate 
about  its  cells.  Axones  of  the  chief  nucleus  enter  the  opposite 
medial  fillet  and  medial  longitudinal  bundle  and  the  homo- 
lateral restiform  body.  Lateral  to  the  principal  nucleus 
are  the  nucleus  of  Deiters  and  the  nucleus  of  the  descending  root. 
Deiters's  nucleus  is  spread  along  the  medial  surface  of  the  resti- 
form body,  chiefly  in  the  pons.  It  becomes  a  distinct  nucleus 
as  the  lower  border  of  the  pons  is  approached  and  grows  larger 
for  some  distance  above  that  point.  In  the  pons  it  is  bent 
backward  with  the  restiform  body  toward  the  cerebellum.  Its 
upper  end  is  thus  placed  in  the  lateral  wall  of  the  fourth  ventricle 
between  the  restiform  body  and  the  brachium  conjunctivum. 
This  portion  is  called  the  superior  nucleus  (of  Bechterew  or 
Flechsig).  Deiters's  nucleus  is  made  up  of  cell-bodies  which 
are  large  in  comparison  with  those  of  the  principal  nucleus.  It 
receives  vestibular  nerve  fibers  and  the  descending  fibers  of 
the  fastigio-bulbar  tract  from  cerebellar  ganglia  and  originates 
fibers  that  enter  the  medial  longitudinal  bundle,  the  vestibulo- 
spinal tract  and  the  restiform  body — all  on  the  same  side.  The 
nucleus  of  Deiters  is  a  relay  in  the  cerebello-spinal  path  and 
it  constitutes  the  middle  link  in  static  arcs  formed  by  the 
vestibular  nerve,  the  Deiters's  neurones  and  motor  nerves.  The 
nucleus  of  the  descending  root  is  the  spinal  nucleus  of  the  vestibular 
nerve.  It  is  composed  of  cell-bodies  scattered  through  a  strand 
of  fibers  called  the  descending  root  which  extends  from  the 
level  of  the  principal  nucleus  down  to  the  nucleus  funiculi 
cuneati  (Bruce).     It  is  placed  somewhat  under  cover  of  the 


CONNECTIONS   OF  VESTIBULAR  NUCLEI 


349 


medial  border  of  the  restiform  body  and,  with  the  enveloping 
descending  root,  separates  this  body  from  the  principal  nucleus. 
Certain  fibers  of  the  descending  root  terminate  in  the  nucleus 
of  the  same  name;  others  in  the  nucleus  of  Deiters.  Axones  of 
the  spinal  nucleus  run  into  the  medial  longitudinal  bundle 


Fig.  130. — Diagrammatic  section  of  medulla  at  the  fillet  decussation;  descend- 
ing tracts  are  red  and  ascending  tracts  are  blue;  gray  matter  is  light. 
a.  Nucleus  gracilis,  b.  Nucleus  cuneatus.  c.  Nucleus  of  the  spinal  tract  of  the  tri- 
geminal nerve.  _  d.  Field  occupied  by  the  rubro-spinal,  thalamo-spinal,  lateral  tecto-spinal 
and  reticulo-spinal  tracts,  e.  Lateral  fasciculus  proprius.  f.  Inferior  end  of  olivary 
nucleus,  g.  Spino-olivary  tract.  12.  Hypoglossal  nerve,  h.  Medial  accessory  olivary 
nucleus.  1.  Pyramid,  j.  Fillet  decussation,  k.  Funiculus  gracilis.  1.  Funiculus  cunea- 
tus. m.  Spinal  tract  of  the  trigeminal  nerve,  n.  Medial  longitudinal  fasc.  o.  Dorsal 
spino-cerebellar  tract,  p.  Ventral  spino-cerebellar  and  spino-thalamic  tracts,  q.  Vesti- 
bulo-sf)inal  tract,     r.  Anterior  tecto-spinal  tract. 


and  restiform  body  of  the  same  side,  proceeding  to  motor 
nuclei  and  the  cerebellar  cortex. 

Cortical  Connection. — Axones  from  the  chief  vestibular 
nucleus  ascend  to  the  thalamus  through  the  opposite  medial 
fillet   whence   the  path  is  completed  by  the  cortical    fillet. 


350  THE   RHOMBENCEPHALON 

Simple  reflex  connections  are  established,  first,  by  axones  of  all 
three  nuclei  which  enter  the  medial  longitudinal  bundles  and, 
dividing  T-like,  ascend  and  descend  to  motor  nuclei;  and 
second,  by  axones  of  Deiters's  nucleus  which  descend  to  spinal 
motor  nuclei.  Coordinated  reflex  connections  are  established 
through  the  cerebellum  as  follows:  some  vestibular  fibers 
run  directly  through  the  restiform  body  to  nucleus  fastigii; 
nucleo-cerebellar  fibers  go  from  each  vestibular  nucleus  to 
cerebellar  cortex;  cortical  axones  from  the  Purkinje  cells 
terminate  in  the  cerebellar  nuclei  from  which  point  the  path 
is  double;  axones  of  nucleus  fastigii  descend  to  Deiters's  nu- 
cleus, whose  axones  reach  the  motor  nuclei  of  spinal  nerves ;  and 
axones  of  nucleus  dentatus  proceed  through  brachium  con- 
junctivum  to  red  nucleus  and  thalamus,  from  which  the  rubro- 
spinal tract  and  thalamo-spinal  tract  establish  a  wide  con- 
nection with  motor  nuclei.  In  both  the  fastigio-bulbar  tract 
and  the  brachium  conjunctivum  there  are  cerebello-tegmental 
fibers  which  go  directly  to  motor  nuclei  of  the  mid-brain,  pons 
and  medulla;  and,  therefore,  belong  to  the  coordinated  reflex 
mechanism. 

Cochlear  Nuclei  {nn.  nervi  cochlearis,  Fig.  123). — There  are 
two  cochlear  nuclei,  the  ventral  and  the  lateral.  They  concern 
hearing  proper.  They  receive  the  terminals  of  the  cochlear 
nerve  and  are  somatic  special  sense  nuclei. 

The  ventral  cochlear  nucleus  appears  in  section  as  a  triangular 
mass  of  cell-bodies  imbedded  in  the  medulla  at  the  upper  end 
of  the  posterior  lateral  sulcus.  It  lies  between  the  restiform 
body  and  the  olive;  the  vestibular  root  of  the  auditory  nerve 
separates  it  from  the  olive.  It  receives  the  greater  number  of 
fibers  in  the  cochlear  nerve  and  gives  rise  to  those  of  the  trape- 
zoid body  and  through  that  to  a  large  part  of  the  lateral  fillet 
of  the  opposite  side;  a  few  of  its  fibers  enter  the  fillet  of  the 
same  side.  In  the  corpus  trapezoideum,  the  cochlear  tract  is 
largely  relayed  by  the  neurones  forming  the  nuclei  of  the  superior 
olivary  group.  The  lateral  cochlear  nucleus  embraces  the  outer 
surface  of  the  restiform  body.  It  is  situated  both  lateral  and 
dorsal    to    the   ventral   nucleus    and,    stretching   around    the 


SPECIAL   NUCLEI   OF    MEDULLA  35 1 

posterior  surface  of  the  restiform  body,  it  produces  the  ventricu- 
lar eminence  in  the  lateral  part  of  the  acustic  area,  called 
the  tuherculum  acusticum.  The  lateral  nucleus  receives  that 
part  of  the  cochlear  root  which  does  not  end  in  the  ventral 
nucleus  and  the  fibers  arborize  about  its  cells.  The  axones 
of  the  lateral  nucleus  form  the  medullary  striae;  a  few  of  them 
enter  the  trapezoid  body  (Figs.  112,119  ^^^  123).  The  medul- 
lary striae  run  somewhat  obliquely  across  the  ventricular  floor 
to  the  median  groove,  plunge  forward  to  the  superior  olivary 
nucleus  of  the  opposite  side  where  they  are  partially  relayed 
and  then,  bending  upward,  are  continued  in  the  lateral  fillet. 
At  the  superior  olivary  nuclei  of  the  opposite  side  the  fibers  from 
the  lateral  and  ventral  nuclei  become  intermingled,  hence  the 
trapezoid  body  and  medullary  striae  combine  in  the  formation  of 
the  lateral  fillet.  The  lateral  fillet  suffers  a  partial  relay  in  its 
own  nucleus,  after  which  it  separates  into  two  parts;  the  prin- 
cipal part  runs  to  the  medial  geniculate  body  by  way  of  the 
brachium  inferius;  the  smaller  part  ends  in  the  quadrigeminal 
colliculi,  chiefly  in  the  inferior  colKculus  on  the  same  side. 
From  the  medial  geniculate  body  to  the  transverse  and  superior 
temporal  gyri  the  acustic  path  is  formed  by  the  acustic  radia- 
tion. This  completes  the  cortical  connection  of  the  cochlear 
nuclei.  Their  reflex  connections  are  established,  first,  by  the 
olivary  pedicle  and  medial  longitudinal  bundle  and,  second,  by 
that  part  of  the  lateral  fillet  which  ends  in  the  colliculi  of  the 
corpora  quadrigemina  and  the  tecto-spinal  tracts  (see  pp.  155 
and  164). 

3.  There  are  Certain  Special  Ntltlei  of  the  Medulla. — 
These  are  not  represented  either  in  the  pons  above  or  the 
spinal  cord  below.  They  are  the  nucleus  funiculi  gracilis,  the 
nucleus  funiculi  cuneati  and  the  nucleus  ohvaris  inferior. 

Nucleus  Funiculi  Gracilis  and  Nucleus  Funiculi  Cuneati  (Figs. 
125  and  126). — The  nucleus  funiculi  gracilis  and  nucleus  funiculi 
cuneati  are  large  nuclei,  extending  from  the  level  of  the  olive  to 
the  lower  end  of  the  medulla.  They  are  situated  near  the 
posterior  surface  beneath  the  gracile  and  cuneate  funiculi, 
whose  fibers  terminate  in  them;  they  give  origin  to  the  medial 


352 


THE   RHOMBENCEPHALON 


fillet,  and  the  anterior  and  posterior  external  arcuate  fibers^  and 
they  produce,  respectively,  the  clava  and  cuneate  tubercle  on  the 
posterior  surface  of  the  medulla.  In  successive  sections  from 
below  upward  the  nucleus  funiculi  gracilis  is  first  seen  as  an 
isolated   mass   of  gray   substance  imbedded  in  the  funiculus 


Fig.  131. — Section  of  medulla  at   the  pyramidal  decussation,  Weigert-Pal 

stain;  meduUated  fibers  are  black  and  gray  substance  is  white. 
a.  Nucleus  gracilis,  b.  Nucleus  cuneatus.  c.  Nucleus  of  the  spinal  tract  of  the  tri- 
geminal nerve,  d.  Beginning  of  anterior  column  of  gray  matter,  e.  Pyramidal  decussa- 
tion. £.  Funiculus  gracilis,  g.  Funiculus  cuneatus.  h.  Spinal  tract  of  the  trigeminal 
nerve,  i.  Field  of  the  spino-cerebellar  and  spino-thalamic  tracts,  j.  Region  of  the  vesti- 
bulo-spinal  tract. 


gracilis  at  the  level  of  the  pyramidal  decussation:  It  enlarges 
dorso-ventrally  and  transversely  toward  its  upper  end,  as  is 
shown  in  consecutive  sections  and  reaches  its  greatest  size  at 
the  clava  where  it  receives  the  terminal  end-tufts  of  the 
funiculus  gracilis.     Very  soon  the  ventral  border  of  the  nucleus 


SOMATIC   TERMINAL   NUCLEI  353 

funiculi  gracilis  fuses  with  the  gray  matter  about  the  central 
canal.  The  axones  of  this  nucleus  form  about  one-half  of  the 
medial  fillet  and  the  external  arcuate  fibers.  The  nucleus 
funiculi  cuneati  (Fig.  126)  appears  at  the  same  inferior  level  as 
the  nucleus  funiculi  gracilis.  It  is  from  the  first  and  throughout 
its  length  continuous  with  the  central  gray  substance  on  which 
it  appears  as  a  bud-like  outgrowth  in  the  lower  medulla.  It 
gradually  broadens  and  elongates  dorsalward  when  traced  up- 
ward (Fig.  125).  Beneath  the  cuneate  tubercle  it  reaches  its  full 
stature  and  gathers  into  itself  the  fibers  of  the  funiculus  cunea- 
tus ;  thence  it  sends  its  own  axones  upward  in  the  medial  fillet 
and  the  external  arcuate  fibers.  Near  the  lower  end  of  the 
medulla  there  is  a  small  lateral  bud  of  gray  matter  connected 
with  the  nucleus  funiculi  cuneati  to  which  it  is  accessory  and, 
like  it,  is  imbedded  in  the  funiculus  cuneatus.  It  is  called  the 
accessory  nucleus  funiculi  cuneati. 

With  entire  accuracy  and  greater  convenience,  these  nuclei 
may  be  called  nucleus  gracilis  and  nucleus  cuneatus.  They  are 
somatic  terminal  nuclei  of  spinal  nerves. 

The  nuclei  gracihs  et  cuneatus  form  the  first  relay  station 
in  the  spino-cerebral  path  for  impressions  of  the  muscular  sense 
and  tactile  discrimination,  and  lesions  in  them  cause  ataxia. 
They  also  lie  at  the  dividing  of  the  ways;  the  direct  path  con- 
tinuing through  the  fillet  decussation  and  the  medial  fillet  to 
the  thalamus,  and  the  indirect  path  running  through  the  arcu- 
ate fibers  to  the  cerebellar  cortex. 

Cortical  Connection. — From  the  cerebellar  cortex  the  impulses 
proceed  cerebral  ward  through  Purkinje's  neurones  to  the 
dentate  nucleus  and  thence  through  the  dentate  neurones  by 
way  of  the  brachium  conjunctivum  cerebelli  to  the  opposite  red 
nucleus  and  thalamus.  The  cortical  fillet  conducts  all  common 
sensory  impulses  from  the  thalamus  to  the  cerebral  cortex. 

Reflex  Connections. — En  route  through  the  cerebellar  cortex, 
coordinating  reflex  impulses  are  excited  which  proceed  through 
cortical  axones  of  the  Purkinje  cells  to  the  nuclei  of  the  cerebel- 
lum; and  then  from  those  nuclei  through  the  cerebello-teg- 
mental  axones  in  the  restiform  body  and  brachium  conjunc- 
23 


354  THE   RHOMBENCEPHALON 

tivum,  first,  directly  to  motor  nuclei  of  the  brain-stem  and 
second,  through  the  intermediation  of  the  rubro-spinal,  thalamo- 
spinal  and  vestibulo-spinal  tracts,  to  the  motor  nuclei  of  all 
cranial  and  spinal  nerves. 

The  nucleus   olivaris  inferior,    the   olivary   nucleus   of   the 
medulla  (Figs.  123  and  125)  is  a  sinuous,  pouch-like  collection  of 
gray  matter  resembling  the  nucleus  dentatus  of  the  cerebellum. 
It  is  situated  near  the  lateral  surface  of  the  medulla  and  is 
invested  superficially  and  deeply  by  fibers  from   the   lateral 
fasciculus  proprius.     Its  open  hilus  looks  medially  and  is  filled 
with  fibers,  the  olivo-cerebellar  fibers,  which  join  it  to  the  opposite 
hemisphere  of  the  cerebellum.     On  either  side  of  the  olivary 
nucleus  is  an  accessory  nucleus — the  medial  accessory,  in  the 
anterior  column  among  the  fibers  of  the  interolivary  part  of  the 
medial  fillet,  and  the  dorsal  accessory  in  the  lateral  column.     The 
olivary  nucleus,   covered  by  fibers  of   the  lateral  fasciculus 
proprius,  forms  the  olive  (oliva).     The  olive  shows  the  longi- 
tudinal extent  of  the  nucleus  and  on  section  it  is  seen  to  measure 
6  mm.  (0.25  inch)  in  depth.     The  olivary  nucleus  is  said  to  be  a 
modern  structure;  it  is  found  well  developed  only  in  the  higher 
mammals.     It  is  a  relay  station  between  the  cerebrum  and  the 
cerebellum  and  between  the  spinal  cord  and  the  cerebellum. 
It  receives  the  thalamo-olivary  fasciculus  from  the  cerebrum 
and  the  spino-olivary  fasciculus  (triangular  tract  of  Helwig) 
from  the  spinal  cord ;  axones  of  the  nucleus  gracilis  and  nucleus 
cuneatus  also  terminate  in  it.     The  cell-bodies  of  the  nucleus 
are  small;  they  give  off  very  rich  dendritic  processes  from  all 
sides,  which  are  closely  massed  about  the  cell-bodies,  and  a 
single,  slender  axone  from  each  cell-body.     The  axones  issue 
largely  from  the  hilus  of  the  nucleus  as  olivary  peduncle;  others 
emerge  from  the  medial  lamina  of  the  olivary  nucleus;  nearly 
all  the  axones  cross  the  median  raphe  and,  piercing  the  opposite 
nucleus,  continue  as  olivo-cerebellar  fasciculus  to  the  cortex  of 
the  cerebellar  hemisphere  and  worm.     According  to  Holmes  and 
Stewart  the  olivo-cerebellar  fibers  have  a  definite  arrangement; 
those  from  the  dorsal  fold  end  in  the  cortex  of  the  superior  sur- 
face, while  those  from  the  ventral  fold  terminate  in  the  inferior 


EMIGRANTS    FROM   RHOMBIC   LIP 


355 


surface;  fibers  from  the  lateral  part  of  the  nucleus  end  in  the 
lateral  part  of  the  hemisphere,  and  fibers  from  the  region  of 
the  hilus  and  from  the  medial  accessory  nucleus  terminate  within 
the  worm  and  the  medial  portion  of  the  hemisphere.     By  far 


f  g 

Fig.  132. — Diagrammatic  section  of  the  medulla  at  the  pyramidal  decussa- 
tion; motor  fibers  and  descending  tracts  are  in  red  and  sensory  fibers  and  as- 
cending tracts  are  in  blue,  gray  matter  remains  light. 

a.  Nucleus  gracilis,  b.  Nucleus  cuneatus.  c.  Nucleus  of  spinal  tract  of  the  trigeminal 
nerve,  d.  Ventral  spino-cerebellar  and  spino-thalamic  tracts,  e.  Spino-olivary  tract. 
f.  Medial  longitudinal  fasc.  g.  Pyramidal  decussation,  h.  Funciculus  gracilis,  i.  Funic- 
sulus  cuneatus.  j.  Spinal  tract  of  the  trigeminal  nerve,  k.  Dorsal  spino-cerebellar  tract. 
1.  Lateral  fasciculus  proprius.  m.  Field  of  rubro-spinal,  thalamo-spinal,  lateral  tecto- 
pinal  and  lateral  recticulo-spinal  tracts  .    n.  Anterior  tecto-spinal  tract. 

the  larger  number  of  fibers  decussate  to  the  opposite  side 
(Brain,  Vol.  31). 

The  neurones  of  the  inferior  olivary  nuclei  are  emigrants  from  the  rhom- 
bic lip.  The  cells  reach  their  positions  through  the  olivo-arcuate  migra- 
tion (Essick),  which  begins  early  in  the  second  month  (in  a  20  mm.  foetus) 
and  continues  into  the  third  month  (143  mm.  foetus).     The  nucleus  is  well 


356  THE   EHOMBENCEPHALON 

outlined  at  the  end  of  the  second  month,  though  it  possesses  but  a  small 
part  of  its  full  quota  of  cells.  At  first  the  migration  is  intramedullary 
only,  later  it  is  in  part  superficial.  The  cell-bodies  cross  the  median  plane, 
impelled  by  the  growing  axones;  with  the  development  of  the  cerebellum, 
the  axones  extend  through  the  restiform  body  to  the  hemispheres  and 
vermis  cerebelli;  these,  with  other  fibers  entering  the  cerebellum,  bear 
along  with  them  from  the  rhombic  Hp  the  stellate  and  granular  cells  of  the 
cerebellar  cortex. 

Lesions  in  the  medulla  are  very  fatal  and  death  usually  occurs 
before  any  sensory  or  motor  phenomena  can  be  observed;  but 
rarely  the  pyramidal  tracts  alone  have  been  involved  or  the 
pyramidal  tracts  together  with  one  or  more  of  the  roots  of  the 
ninth  to  the  twelfth  cerebral  nerves.  In  the  last  case,  crossed 
paralysis  is  produced,  as  in  the  pons,  affecting  the  cerebral 
nerves  on  the  same  side  and  the  opposite  spinal  nerves.  In 
progressive  bulbar  paralysis  the  motor  nuclei  of  the  medulla  are 
involved  as  a  preliminary  to  the  degeneration  of  the  anterior 
gray  columna  in  the  spinal  cord. 

RHOMBENCEPHALON 
SECTION  IV.    THE  FOURTH  VENTRICLE 

The  common  cavity  of  the  rhombencephalon  is  the  fourth 
ventricle  (ventriculus  quartus)  (Fig.  112).  The  fourth  ventricle 
is  dorsal  to  the  pons  and  medulla,  and  is  ventral  to  the  cere- 
bellum (Fig.  104).  It  is  broadest  at  the  junction  of  the  pons 
and  medulla  (Figs.  112  and  122).  Above  and  below  that  junction, 
it  gradually  contracts  to  the  size  of  the  cerebral  aqueduct  and 
central  canal  of  the  spinal  cord,  with  which  it  is  continuous. 
Inferiorly  it  communicates  through  its  roof  with  the  subarach- 
noid space  via  three  apertures,  a  median  and  two  lateral.  The 
fourth  ventricle  is  a  gable-roofed  chamber  with  a  diamond-shaped 

Description  to  Fig.  133. 

a.  Nucleus  of  olfactory  nerves,  b.  Nucleus  of  oculomotor  nerve,  c.  Nucleus  of  trochlear 
nerve,  d.  Nucleus  of  descending  root  of  trigeminus,  e.  Chief  motor  nucleus  of  trigeminus. 
f .  Nucleus  of  facial,  g.  Nucleus  of  abducens.  h.  Nucleus  ambiguus  (accessory,  vagus  and 
glossopharyngeus).  i.  Nucleus  of  hypoglossus.  j.  Nucleus  of  accessory  nerve.  Nuclei  of 
optic  nerve,  k.  Pulvinar  of  thalamus.  1.  Lateral  geniculate  body.  m.  Nucleus  of  superior 
coUiculus.  n.  Sensory  nucleus  of  trigeminus,  o.  Nucleus  of  vestibular  nerve,  p.  Ventral 
nucleus  of  cochlear  nerve,  q.  Lateral  nucleus  of  cochlear  nerve,  r.  Nucleus  alae  cinereae 
(vagus  and  glossopharyngeus).  s.  Solitary  tract  (intermediate  and  glossopharyngeus).  t. 
Nucleus  of  spinal  tract  of  trigeminus. 


CRANIAL   NERVE   NUCLEI 


357 


Fig.  133. — Nuclei  of  the  cerebral  nerves  in  the  medulla,  pons,  mid-brain,  inter- 
brainand  olfactory  bulb.  Motor  (or  genetic)  nuclei,  red;  terminal  (or  sensory) 
nuclei,  blue.     (After  Morris's  Anatomy.) 


358  THE    RHOMBENCEPHALON 

floor.  The  gables  (Fig.  104)  are  directed  lateralward  and  are 
prolonged  in  tunnel-like  extensions  around  the  restiform  body 
forming  the  lateral  recess.  The  long  axis  of  the  ventricular  floor 
(Fig.  112  and  133)  is  parallel  with  the  spinal  cord,  and  extends 
from  the  superior  extremity  of  the  pons  to  the  middle  of  the 
medulla.  The  transverse  axis  coincides  with  the  junction  of  the 
pons  and  medulla.  Thus  the  superior  triangle  of  the  floor  is 
formed  by  the  pons;  the  inferior,  by  the  medulla  oblongata. 
The  fourth  ventricle  is  lined  with  ependyma,  which  is  complete 
throughout,  except  in  the  roof  of  the  inferior  part,  where  below 
the  inferior  medullary  velum  only  the  epithelial  layer  is  present. 

Boundaries. — The  floor  is  formed  by  the  pons  and  medulla. 
The  lateral  wall  (superior  triangle)  is  formed  by  the  brachium 
conjunctivum  of  the  cerebellum;  and  (inferior  triangle)  by  the 
taenia  of  the  fourth  ventricle  winding  across  the  restiform  body, 
funiculus  cuneatus  and  funiculus  gracilis  to  the  oheoc.  The  roof 
is  formed  by  the  superior  medullary  velum  (valve  of  Vieussens) 
superiorly;  and  by  the  inferior  medullary  velum  and  roof  epithe- 
lium, inferiorly  (Fig.  122).  The  superior  and  inferior  halves  of 
the  roof  meet  at  an  acute  angle,  the  fasti  gium,  and  form  the  peak 
of  the  fourth  ventricle  (Fig.  104).  On  either  side  the  gable  is 
pushed  out  over  the  restiform  body  and  thus  is  formed  the 
lateral  recess.  The  lateral  recess  is  a  tunnel-like  extension  of 
the  ventricular  cavity,  reaching  almost  to  the  posterior  lateral 
sulcus.  The  recess  is  bounded  superiorly  and  ventrally  by 
the  restiform  body;  dorsally  by  the  inferior  medullary  velum 
and  inferiorly  by  the  roof  epithelium.  The  chorioid  plexuses 
of  the  fourth  ventricle  invaginate  the  roof  epithelium  and  hang 
from  the  roof  into  the  lateral  recesses  and  the  inferior  part  of  the 
cavity  (Fig.  122). 

Floor  of  the  Fourth  Ventricle  {fossa  rhomhoidea). — Because 
it  contains  the  nuclei  of  one  or  more  roots  of  the  posterior  eight 
(fifth  to  twelfth)  cerebral  nerves,  the  floor  of  the  fourth  ven- 
tricle is  a  very  important  area  (Figs.  112  and  133).  A  median 
groove  bounded  by  the  eminentiae  mediales  forms  the  long  axis 
of  the  diamond-shaped  floor  and  divides  it  into  two  lateral 
halves;  the  medial  eminences  form  prominent  features  of  the 


FLOOR  OF  FOURTH  VENTRICLE  359 

ventricular  floor.  They  are  broadest  in  the  middle;  they  taper 
to  a  point  in  the  lower  angle  of  the  ventricle  like  the  nibs  of  a 
pen  and  they  are  bounded  laterally  by  an  important  sulcus, 
the  sulcus  limitans,  which  widens  out  at  two  points  into  small 
fossae,  the  fovea  superior  in  the  pons  smd  the  fovea  inferior  in  the 
medulla.  The  sulcus  limitans  separates  the  ventral  zone 
(efiferent)  from  the  dorsal  zone  (afferent)  in  the  embryo;  and  in 
the  adult  it  intervenes  between  the  two  regions  containing 
genetic  and  terminal  nuclei.  The  ventricular  floor  is  bisected 
transversely  by  a  number  of  lines,  the  medullary  striae  (striae 
medullares) .  The  striae  are  produced  by  bundles  of  fibers  which 
rise  from  the  lateral  cochlear  nucleus  of  the  auditory  nerve. 
Diverging  somewhat  and  plunging  into  the  medulla  and  pons 
at  the  median  groove  the  fibers  of  the  striae  enter  the  opposite 
trapezoid  body  and  lateral  fillet.  The  medullary  striae  divide 
each  lateral  half  of  the  floor  into  a  superior  and  an  inferior 
triangle. 

The  superior  triangle  of  the  floor  presents  the  colliculus 
facialis,  superior  fovea,  locus  caeruleus  and  a  part  of  the  acustic 
area. 

The  colliculus  facialis  (Fig.  112)  in  the  superior  part  of  the 
eminentia  medialis,  is  located  next  the  median  groove.  It  is 
produced  largely  by  the  genu  of  the  facial  nerve.  Beneath  it  is 
the  nucleus  of  the  abducent  (sixth)  nerve  (Fig.  133).  Lateral 
to  it  and  above  the  striae  medullares  is  a  small  fossa,  the  fovea 
superior. 

Fovea  Superior  (Fig.  112) . — The  fovea  superior  is  near  the 
lateral  wall  of  the  ventricle  and  marks  the  location  of  the  facial 
nucleus  (seventh)  and  ventro-medial  to  that  the  salivary 
nucleus  of  the  intermediate  nerve  which  are  deeply  seated  in 
the  pons.  Running  upward  along  the  wall  of  the  ventricle 
from  the  superior  fovea  is  the  sulcus  limitans.  It  is  a  blue- 
floored  groove  in  the  pons  called  locus  caeruleus. 

The  locus  cceruleus  (Fig.  112)  continues  to  the  superior  angle 
of  the  ventricle.  The  blue  color  is  due  to  the  substantia  fer- 
ruginea,  a  pigmented  layer  of  cell-bodies  underlying  the 
ependyma.     The  principal    motor  nucleus    of    the  trigeminal 


360  THE   RHOMBENCEPHALON 

nerve  (fifth)  lies  beneath  the  superior  part  of  the  locus  caeruleus 
but  is  not  formed  by  the  substantia  ferruginea  (Fig.  133). 

Inferior  Triangle  of  the  Ventricular  Floor. — It  presents 
The  trigonum  hypoglossi,  fovea  inferior,  ala  cinerea  and  emi- 
nentia  cinerea,  and  most  of  the  area  acustica  (Fig.  112). 

The  hypoglossal  triangle  (Fig.  112)  is  produced  by  the  inferior 
half  of  the  eminentia  medialis.  Its  apex  is  in  the  inferior  angle 
of  the  ventricle  and  forms  one  nib  of  the  calamus  scriptorius; 
its  base  looks  upward  and  is  situated  under  the  medullary 
striae.  The  twelfth  nerve  rises  from  the  column  of  cells  whose 
upper  one-half  is  covered  by  it  and  it  also  covers  the  nucleus 
intercalatus  (Streeter)  (Fig.  133).  Lateral  to  the  trigonum 
hypoglossi  and  inferior  to  the  striae  medullares  is  the  inferior 
fovea  which  forms  the  apex  of  the  ala  cinerea. 

Ala  Cinerea  {trigonum  vagi,  Fig.  112). — The  vagus  triangle 
is  of  a  darker  color  than  the  ventricular  floor  around  it,  hence 
the  name  ala  cinerea.  The  inferior  fovea  forms  the  depressed 
and  superiorly  directed  apex  of  the  ala;  its  floor  rises  inferiorly 
to  the  base,  eminentia  cinerea,  which  is  directed  toward  the  clava. 
The  nucleus  alae  cinereae,  with  nucleus  cardiacus  in  its  middle 
part,  and  the  nucleus  tractus  solitarii,  two  nearly  parallel 
columns  of  cell-bodies,  15  mm.  in  length,  are  in  part  covered 
by  the  ala  cinerea  (Fig.  133).  These  nuclei  are  located  in  the 
gelatinous  gray  substance  near  the  ventricle.  Deep  in  the 
formatio  reticularis  lies  the  nucleus  ambiguus,  a  large  column 
of  cells  2  cm.  long;  a  portion  of  its  upper  half  is  covered  by 
the  ala  cinerea.  The  nucleus  salivarius  is  also  located  in  the 
reticular  formation;  it  lies  in  the  upper  medulla  ventral  to 
sulcus  limitans. 

Area  Postrema. — Below  the  ala  cinerea  and  between  it  and  the 
taenia  ventriculi  quarti  there  is  a  small  fusiform  strip  of  the 
ventricular  floor  which  Retzius  has  called  the  area  postrema. 
An  oblique  stria  separates  it  from  the  base  of  the  ala  cinerea. 

The  area  acustica  occupies  the  lateral  angle  of  the  ventricular 
floor  (Fig.  112).  It  is  partly  in  the  superior  triangle,  but  chiefly 
in  the  inferior.  It  is  an  irregular  triangle:  its  base  is  on  the 
sulcus  limitans,  its  apex  lies  in  the  lateral  recess  of  the  ventricle 


GENESIS   OF   CRANIAL  NERVES  36 1 

and  its  sides  are  formed  by  the  taenia  and  the  restiform  body. 
The  acustic  triangle  is  crossed  by  the  medullary  striae.  A 
slight  eminence,  the  tuber culum  acusticum,  makes  the  lateral 
angle  of  the  acustic  area  most  prominent.  Beneath  the  acustic 
area  are  the  vestibular  nuclei  of  the  auditory  nerve;  also  the 
lateral  part  of  the  cochlear  nucleus,  which  is  found  in  the 
acustic  tubercle  (Fig.  133). 

ORIGIN  OF  CEREBRAL  OR  CRANIAL  NERVES 

According  to  Sommering  there  are  twelve  pairs  of  cerebral 
nerves  (nervi  cerebrales) ,  but  to  this  must  be  added  the  nervus 
intermedins  (pars  intermedia)  which,  though  associated  with 
the  facial  nerve  in  the  facial  canal,  is  of  itself  a  true  mixed  nerve. 
The  remnant  of  a  nervus  terminalis  should  also  be  included. 
The  first,  second  and  eighth  cerebral  nerves  are  purely  sensory ; 
six  of  them,  the  third^  fourth,  sixth,  seventh,  eleventh  and 
twelfth,  are  purely  motor;  while  the  fifth,  the  intermediate,  the 
ninth  and  tenth  are  mixed  nerves  and  contain  both  efferent  and 
afferent  fibers. 

Cerebral  Nerves,  Nervi  Cerebrales  (Figs,  in  and  133). — 

1.  Olfactory  (nn.  olfactorii) — special  sense  of  smell. 

2.  Optic  (n.  opticus) — special  sense  of  sight. 

3.  Oculomotor  (n.  oculomotorius) — motor. 

4.  Trochlear  (n.  trochlearis) — motor. 

5.  Trigeminal  (n.  trigeminus) — motor  and  common  sensory. 

6.  Abducent  (n.  abducens) — motor. 

7.  Facial  (n.  facialis) — motor. 

Intermediate    (n.    intermedins) — special  sense  of  taste, 
secretory  and  trophic.     The  glossopalatine  nerve. 

8.  Acustic  (n.  acusticus) — special  senses  of  hearing  and 

equilibrium. 

9.  Glossopharyngeal  (n.  glossopharyngeus) — Special  sense  of 

taste,  common  sensory,  secretory,  trophic  and  motor. 

10.  Vagus    (n.  vagus) — motor,  vaso-motor,  viscero-motor, 

inhibitory,  secretory,  trophic  and  common  sensory. 

11.  Accessory  (n.  accessorius) — motor. 

12.  Hypoglossal  (n.  hypoglossus) — motor. 


362  THE   RHOMBENCEPHALON 

Robert  Bean  suggests  certain  changes  in  the  treatment  and 
nomenclature  of  cranial  nerves,  most  of  which  could  be  adopted 
with  advantage,  viz.:  ''Masticator  nerve"  instead  of  motor 
root  of  trigeminal,  to  indicate  its  supply  of  the  muscles  of 
mastication;  ''glossopalatine  nerve"  in  place  of  intermediate 
nerve,  because  this  better  describes  its  distribution  to  tongue 
and  palate  (and  glands);  ''acustic  nerve"  should  be  limited  in 
meaning  to  the  nerve  supplying  the  cochlea,  which  alone  is  a 
nerve  of  hearing;  and  the  nerve  distributed  to  the  vestibule  and 
semicircular  canals,  whose  function  is  equilibrium,  should  be 
considered  an  independent  nerve,  ''the  vestibular  nerve" 
(Anat.  Rec,  Vol.  7). 

All  cerebral  nerves  are  connected  with  the  brain  and,  when 
their  functions  were  not  understood,  these  points  of  connection 
were  indiscriminately  called  origins;  but  with  our  present  knowl- 
edge of  the  functions  and  development  of  the  pure  sensory  and 
the  mixed  nerves  such  use  of  the  term  "origin"  is  not  ad- 
missible. Pure  sensory  nerves  and  the  sensory  roots  of  mixed 
nerves  take  their  origins  from  ganglia  situated  wholly  outside 
the  brain.  From  those  ganglia  the  dendrites  grow  outward  to 
the  peripheral  distribution  of  the  respective  nerves;  the  axones 
grow  centrally  into  the  brain,  where  they  arborize  and  end  in 
groups  of  cell-bodies  forming  nuclei.  Such  nerves  conduct 
impulses  from  the  periphery  to  these  nuclei,  hence  the  name 
applied  to  them  is  terminal  nuclei  {nuclei  terminales)  (see  the 
blue  nuclei,  Fig.  133) .  The  motor  nerves  and  the  motor  roots  of 
mixed  nerves  take  their  origins  inside  the  brain  from  groups  of 
cell-bodies  also  called  nuclei.  The  axones  grow  outward  from 
these  latter  nuclei  toward  the  periphery;  they  conduct  impulses 
from  the  nuclei  to  the  muscles  or  to  the  secreting  cells  in  their 
respective  areas  of  distribution,  hence  the  nuclei  of  motor  nerves 
and  motor  roots  are  genetic  nuclei  {nuclei  origines)  (see  the 
red  nuclei,  Fig.  133).  Thus  it  is  seen  that  the  brain  connection 
of  a  motor  nerve  is  its  true  origin,  while  this  connection  is  the 
real  termination  of  a  sensory  nerve. 

In  fishes  the  bodies  of  certain  peripheral  sensory  neurones 
are  found  inside  the  spinal  cord,  the  ganglion  cells  of  Rohon- 


TABLE    OF    NERVES 


363 


Beard,  from  which  the  dendritic  processes  grow  out  of  the  cord 
to  the  periphery;  and  J.  B.  Johnston  claims  that  the  mesen- 
cephaHc  nucleus  of  the  trigeminal  nerve  is  an  example  in  man  of 
a  ganglion  included  within  the  neural  tube.  We  know  this  is 
true  of  the  ganglion  giving  rise  to  the  optic  nerve  and,  if  it  be 
true  of  the  mesencephalic  nucleus,  here  is  another  exception  to 
the  rule  that  ganglia  are  groups  of  cell-bodies  outside  of  the 
neural  tube. 

TABLE  II 

SENSORY  NERVES  AND  SENSORY  ROOTS 


Ganglion  of  Origin 


Olfactory  cells  in  nasal 
mucous  membrane. 


Ganglionar  layer  of   the 
retina. 


Terminal  Nucleus 


Mitral  and  brush  cells 
of  bulb  (a  part  of  cere- 
bral hemisphere). 

Nuclei  of  same  in  inter- 
brain  and  mid-brain. 


Entrance  into  Brain 

I.  Olfactory  {Smell) 
Under  surface  of  olfac- 
tory bulb. 

2.  Optic  {Sight) 
Surface  of  lateral  genic- 
ulate body,  pulvinar 
of  thalamus  and  su- 
perior quadrigeminal 
colliculus. 

5.  Trigeminal  {Sensory  Root) 
Anterior  surface  of  the      Nucleus  tractus  spinalis  n. 
pons.  trigemini   reaching  from 

mid-pons  to  second  cervi- 
cal nerve. 

Intermediate  Nerve  {Sensory  Root)  {Taste) 
Geniculate  ganglion.  Groove  between  pons        Nucleus    tractus    solitarii 

and  medulla,  be- 
tween seventh  and 
eighth  nerves. 


Semilunar  ganglion. 


beneath    inferior    fovea 
in  medulla. 


8.  Acustic  {Hea/ing  and  Equilibrium) 
Cochlear    Root. — Spiral      Groove  between  pons      Cochlear 
and  medulla. 


ganglion  (of  Corti). 


Vestibular  Root. — Vestib- 
ular ganglion. 


Ponto-med- 
uUary  groove. 


Nuclei. — Ventral 
and  lateral,  placed  ven- 
tral and  lateral  to  resti- 
form  body  in  medulla. 
Vestibular  Nuclei. — Princi- 
pal, Deiters's  and  nu- 
cleus of  descending  root, 
in  floor  of  fourth  ventricle 
in  medulla. 


364  THE   RHOMBENCEPHALON 

9.  Glossopharyngeal  {Sensory  Root)  {Taste,  Etc.) 
Superior  and  petrosal        Posterior  lateral  sulcus     Nucleus     tractus     solitarii 
ganglia    in    jugular  of  medulla.  and     nucleus    alse    cin- 

foramen.  ereae  in  medulla. 

10.   Vagus  {Sensory  Root) 
Jugular      and      nodular     Posterior  lateral  sulcus     Nucleus   alae  cinereae,   and 
ganglia      in      jugular        of  medulla.  nucleus    tractus    spinalis 

foramen  and  below  it.  n.  trigemini. 

TABLE  m 

MOTOR  NERVES  AND  MOTOR  ROOTS 

Genetic  Nucleus  Exit  from  Brain 

3.  Oculomotor  {Motor  Nerve) 
Nucleus  in  floor  of  cerebral  aqueduct  in         Interpeduncular   fossa   of   mid-brain, 
mid-brain  under  superior  colliculus. 

4.  Trochlear  {Motor  Nerve) 

Nucleus  in  floor  of  cerebral  aqueduct  Superior  medullary  velum  in  isthmus 
in  njid-brain  under  inferior  coUiculus.  rhombencephali. 

5.  Trigeminal  {Motor  Root) 

Nucleus  in  floor  of  cerebral  aqueduct        Anterior  surface  of  pons, 
in  mid-brain  and  under  locus  caeru- 
leus  of  pons. 

6.  Abducent  {Motor  Nerve) 
Nucleus   under   colliculus   facialis   in         Groove  between  pons  and  medulla, 
pons. 

7.  Facial  {Motor  Nerve) 
Nucleus  under  fovea  superior  in  pons.         Groove  between  pons  and  medulla. 

Intermediate  {Efferent  Part,  Secretory) 
Salivary  nucleus  in  pons.  Groove  between  pons  and  medulla. 

9.  Glossopharyngeal  {Motor  Root) 
Nucleus  salivarius  and  nucleus  am-         Posterior  lateral   sulcus  of   medulla, 
biguus  in  the  medulla.  upper  end. 

10.  Vagus  {Motor  Root) 
Nucleus  alae  cinereae  (n.  cardiacus)  and         Posterior  lateral  sulcus  below  ninth* 
nucleus  ambiguus.  and  between   olive   and  restiform 

body. 

II.  Accessory  {Motor  Nerve) 

Cerebral  Root. — Nucleus  ambiguus  in  Posterior  lateral  sulcus  of  medulla 
closed  medulla.  below  level  of  olive. 

Spinal  Root. — Nucleus  in  lateral  part  Lateral  surface  of  cord  betA^een  liga- 
of  base  of  anterior  columna — upper  mentum  denticulatum  and    poste- 

five  segments  of  cord.  rior  roots  of  spinal  nerves. 


TERMINAL   NERVE  365 

12.  Hypoglossal  {Motor  Nerve) 
Nucleus  under  trigonum  hypoglossi,         Anterior    lateral    sulcus    of    medulla 
floor   of   fourth   ventricle,    and   in  between  pyramid  and  olive, 

closed  medulla. 

Nervus  Terminalis. — The  terminal  nerve  has  been  found  in  fishes,  am- 
phibia, reptiles  and  mammals;  it  is  present  but  vestigial  in  man.  It  is  a 
plexiform  nerve  coursing  along  the  surface  of  the  gyrus  rectus,  medial  to 
the  olfactory  bulb  and  tract;  and,  continuing  through  the  cribriform  plate, 
it  descends  in  the  septal  mucosa  as  far  as  the  vomero-nasal  remnant  and 
anterior  to  it.  It  possesses  a  ganghon,  more  or  less  distributed  along  its 
course,  called  the  ganglion  lerminale.  Its  point  of  attachment  to  the  brain 
is  doubtful:  Johnston,  McKibben,  McCotter  and  others  claim  that  it 
enters  the  infero-medial  part  of  the  fore-brain  in  the  uncinate  region  or 
along  the  medial  border  of  the  trigonum  olfactorium;  Hardesty  suggests 
that  it  may  be  continuous  with  the  cephalic  sympathetic  nerves.  The  gan- 
glion cells  are  small  and  multipolar  in  character;  the  nerve  fibers  are  very 
slender  and  non-meduUated  in  man;  these  facts  and  the  plexiform  nature  of 
the  nerve  indicate  that  its  function  is  autonomic.  The  fibers  are  collected 
into  bundles  surrounded  by  sheath  cells,  like  the  fila  of  the  olfactory  nerve 
(Huber  and  Guild). 

Many  investigators  have  studied  the  terminal  nerve  in  the  lower  forms. 
According  to  Johnston  and  others  it  develops  like  an  ordinary  sensory 
nerve  in  many  selachians;  its  ganglion  is  derived  from  the  neural  crest; 
its  fibers  are  medullated;  its  function  is  apparently  cutaneous  sensibility; 
its  central  processes  enter  the  brain  in  the  uncinate  region  and  terminate  in 
a  nucleus,  which  is  of  vast  importance  in  the  development  of  the  fore-brain. 
Whether  through  a  long  phylogenesis  the  nerve  lost  its  primitive  function 
and  acquired  a  new  and  very  different  function  remains  to  be  determined, 
but  it  appears  to  be  a  sympathetic  nerve  in  man. 

Terminal  Nuclei. — The  terminal  nuclei  of  the  first  and  second 
cerebral  nerves  are  peculiar  and  cannot  as  yet  be  classified  with 
the  nuclei  of  other  sensory  nerves  and  sensory  roots  (Figs.  31, 
55  and  86).  The  terminal  nuclei  of  the  fifth,  the  intermediate, 
the  eighth,  ninth  and  tenth  nerves  may  be  called  the  posterior 
columna  series  because  they  are  formed  by  masses  of  cell-bodies 
representing  the  upward  prolongation  of  the  posterior  columna 
of  gray  substance  in  the  spinal  cord.  The  posterior  columna, 
as  pointed  out  by  Herrick,  contains  two  functional  columns 
of  cells,  a  somatic  and  a  visceral.  The  somatic  column  com- 
prises all  the  posterior  columna  except  its  medio-basal  part, 
called  the  dorsal  nucleus  of  Clark,  that  is  visceral.     The  somatic 


366  THE   RHOMBENCEPHALON 

nuclei  receive  sensory  impulses  as  well  as  impulses  exciting 
reflexes,  while  under  normal  conditions  the  visceral  nuclei 
receive  only  non-sensory  excito-reflex  impulses.  Terminal 
nuclei  are  composed  of  the  bodies  of  afferent  neurones  of  the 
second  order;  they  receive  the  axones  of  first  order  neurones 
which  constitute  the  peripheral  nerves.  Leaving  the  olfactory 
and  optic  terminal  nuclei  out  of  consideration  for  the  present, 
all  terminal  nuclei  give  off  three  systems  of  axones:  (i)  the 
corticipetal  system,  which  runs  toward  the  cerebral  cortex  and 
may  be  divided  into  two  or  more  bundles;  (2)  the  simpler  reflex 
system  which  directly  or  through  the  medial  longitudinal  bundle 
terminate  in  motor  nuclei  and  (3)  the  coordinating  reflex  system, 
which  runs  through  the  restiform  body  to  the  cerebellar  cortex 
and  produces  impulses  of  coordination.  The  corticipetal 
fibers  from  common  sensory  terminal  nuclei  form  several 
specific  strands,  according  to  Head  and  Holmes,  each  of  which 
carries  only  one  particular  variety  of  impulse,  as  tactile  locali- 
zation, tactile  discrimination  of  two  or  more  simultaneous 
contacts,  muscle-sense  (sense  of  posture  and  sense  of  move- 
ment), pain,  pleasure,  hot,  cold,  etc.  However,  these  distinct 
specific  strands  are  collected  into  two  groups  or  strung  on  two 
sets  of  poles;  those  carrying  impulses  of  the  muscle-sense  and 
tactile  discrimination  form  a  part  of  the  medial  fillet;  while  the 
strands  bearing  pain,  temperature  and  localizing  tactile  im- 
pulses join  the  spino- thalamic  tract.  Both  groups  of  corti- 
cipetal axones  terminate  in  the  lateral  nucleus  of  the  thalamus. 
Of  course  the  terminal  nuclei  of  nerves  of  special  sense  form 
specific  tracts;  they  may  or  may  not  be  divided  (Brain,  Vol. 
34).  Terminal  nuclei  are  common  sensory  and  special  sensory. 
Common  Sensory  Nuclei  (Fig.  133). — Of  the  posterior  columna 
series  of  nuclei,  the  terminal  nucleus  of  the  fifth,  a  part  of  the 
tenth  and  a  part  of  the  terminal  nucleus  of  the  ninth  nerve 
receive  common  sensory  impulses,  and  trasmit  them  to  the 
opposite  thalamus  by  two  routes,  viz.,  through  the  medial  fillet 
and  through  the  spino-thalamic  tract.  From  the  thalamus 
these  impulses  are  carried  to  the  cortex  of  the  posterior  central 
gyrus  and  other  gyri.     Thus  is  the  cortical  connection  of  these 


NUCLEI   OF    SPECIAL    SENSE   NERVES  367 

nuclei    established   and    each   is   brought   into    simple    reflex 
connection  with  motor  nuclei  by  axones  of  the  terminal  nuclei 
which    run    chiefly   through   the   medial   longitudinal   bundle 
and  terminate  in  the  motor  nuclei.     Coordinated  reflex  con- 
nection is  made  with  the  cerebellar  cortex  by  axones  which  run 
through  the  restiform  body.     From  the  cortex  of  the  cerebellum 
the  junction  with  motor  nuclei  is  established  by  axones  of  the 
cortical  cells  of  Purkinje,  which  end  in  the  cerebellar  nuclei, 
and  the  cells  of  the  cerebellar  nuclei,  which  form  the  cerebello- 
tegmental  tracts,  assisted  by  the  neurones  of  Deiters's  nucleus, 
of  the  thalamus    and   red   nucleus.     The   cerebello-tegmental 
fibers  go  through  the  brachium  conjunctivum  and  restiform 
body  directly  to  the  cranial  motor  nuclei;  also  to  thalamus,  red 
nucleus    and    the    nucleus    of    Deiters;   axones    of    Deiters's 
nucleus  pass  through  the  medial  longitudinal  bundle  to  cranial 
nerve  nuclei;  and  the  vestibulo-spinal,  rubro-spinal  and  thalamo- 
spinal  tracts  terminate  in  motor  nuclei,  both  spinal  and  cranial. 
Special  Sense  Nuclei. — The  cortical  connection  of  the  nucleus 
tractus  solitarii,  which  receives  taste  impulses  from  the  glosso- 
pharyngeal and  intermediate  nerves,  has  been  definitely  traced 
by  May  and  Horsley;   it  is  relayed  in  the  thalamus  and  is 
established   by   fibers    of  the   soHtary  nucleus  which  extend 
through  the  pons  and  mid-brain  and  by  certain  fibers  of  the 
internal  capsule  which  end  in  the  cingulate  gyrus  (?).     The 
cochlear  nuclei  (ventral  and  lateral)    receive  true  impulses  of 
hearing  and  conduct  them  on  toward  the  cerebral  cortex  by 
way  of  their  axones  which  form  the  trapezoid  body  and  medul- 
lary striae  and  then  unite  in  forming  the  lateral  fillet  (Fig.  119). 
The  remaining  Hnks  of  the  cortical  connection  are  formed  by 
the    brachium   inferius    and    the    acustic   radiation    (radiatio 
acustica).     The  reflex  connection  of  these  nuclei  is  somewhat 
indirect.     It  is  established  in  part  by  certain  fibers  of  the  lateral 
fillet  which  end  in  the  quadrigeminal  colliculi,   together  with 
the  anterior  tecto-spinal  bundle;  but  is  chiefly  brought  about 
by  the  olivary  pedicle  and  the  medial  longitudinal  bundle. 
The   vestibular   nuclei — the    principal    (Schwalbe's),    Deiters's 
and  the  nucleus  of  the  descending  root — concern  equilibrium. 


368  THE  RHOMBENCEPHALON 

They  receive  impulses  from  the  vestibule  and  semicircular 
canals  of  the  internal  ear.  They  have  a  cerebral  and  an  im- 
portant cerebellar  connection.  The  former  is  established  as 
far  as  the  thalamus  by  the  opposite  medial  fillet,  and  com- 
pleted by  the  cortical  fillet;  and  the  latter  is  formed  by  the 
direct  root-fibers  running  to  nucleus  fastigii  of  the  cerebellum 
and  by  nucleo-cerebellar  fibers  going  from  each  of  the  three 
terminal  nuclei  through  the  restiform  body  to  cerebellar  cortex. 
The  coordination  path  is  completed  by  the  cortico-nuclear  fibers 
(of  Purkinje's  cells) ;  the  cerebello-tegmental  fibers;  the  thalamo- 
spinal,  the  rubro-spinal  and  the  vestibulo-spinal  tracts  and 
the  medial  longitudinal  bundle.  The  simple  reflex  connection 
of  the  vestibular  nerve  is  established  by  axones  of  the  vestibu- 
lar nuclei  which  run  to  motor  nuclei  through  medial  longitu- 
dinal bundle  and  vestibulo-spinal  tract. 

The  terminal  nuclei  of  the  optic  nerve  are  situated  in  the  lateral 
geniculate  body,  the  pulvinar  of  the  thalamus  and  the  superior 
colliculus  of  the  corpora  quadrigemina  (Fig.  55).  Like  the  ter- 
minal nucleus  of  the  olfactory  nerve,  these  cannot  at  present  be 
included  in  the  posterior  columna  series,  because  the  ventral  and 
dorsal  zones  of  the  embryonic  fore-brain  have  not  been  suf- 
ficiently elucidated.  If  the  sulcus  hjrpothalamicus  really 
separate  ventral  from  dorsal  zone  in  the  inter-brain,  as  is 
claimed  by  many,  it  would  seem  that  both  the  optic  and  ol- 
factory terminal  nuclei  might  be  included  in  the  posterior  series; 
but  there  is  need  of  further  investigation,  as  this  places  the 
whole  cerebral  hemisphere  in  the  dorsal  zone. 

The  cortical  connection  of  the  terminal  nuclei  of  the  optic 
nerve  (Fig.  90)  is  established  by  fibers  of  the  optic  radiation 
(radiatio  occipito-thalamica)  which  rise  in  the  lateral  geniculate 
body  and  in  the  pulvinar  of  the  thalamus  and  terminate  in  the 
cortex  of  the  calcarine  region  of  the  occipital  lobe.  From  this 
cortical  center  corticifugal  fibers  run  through  the  occipito- 
thalamic  radiation  and  brachium  superius  to  the  superior  quad- 
rigeminal  colliculus.  This  colliculus  also  receives  a  few  fibers 
directly  from  the  outer  root  of  the  optic  tract;  it  thus  becomes 
the  center  of  optic  reflexes;  and  axones  of  the  superior  colliculus 


OLFACTORY   CONNECTIONS  369 

form  the  anterior  tecto-spinal  bundle  which  completes  the 
connection  with  opposite  motor  nuclei.  The  terminal  optic 
nuclei  are  connected  with  the  cerebellum  by  those  nucleo-cere- 
bellar  fibers  which  rise  in  these  nuclei;  they  descend  to  the  cere- 
bellar cortex  through  the  brachium  conjunctivum  and  the  re- 
maining links  of  the  coordinating  reflex  arcs,  which  join  the 
cerebellar  cortex  to  motor  nuclei,  are  fully  set  forth  in  the  pre- 
ceding paragraphs. 

The  terminal  nucleus  of  the  olfactory  nerve  is  situated  in  the 
olfactory  bulb  (Figs.  31  and  86).  This  nucleus  is  connected 
with  the  cortical  center  in  the  hippocampal  formation  and  with  the 
amygdalate  and  habenular  nuclei  by  the  olfactory  tract  and 
striae-lateral,  intermediate  and  medial  (see  p.  76).  Reflex 
Connection. — In  man  there  is  the  remnant  of  a  very  com- 
plicated mechanism  of  olfactory  reflexes.  Some  of  its  principal 
tracts  are  the  following:  the  hippocampo-mammillary  fasciculus, 
the  fasciculus  mammillaris  princeps,  the  mammillo-thalamic 
and  thalamo-spinal  fasciculi;  the  mammillo-tegmental  fas- 
ciculus, the  mammillary  peduncle,  and  the  dorsal  longitudinal 
bundle  of  Schiitz  to  genetic  nuclei;  the  olfacto-  and  hippocampo- 
habenular  fasciculi,  the  habenulo-peduncular  fasciculus,  the 
interpedunculo-tegmental  fasciculus,  and  both  the  dorsal 
longitudinal  bundle  of  Schiitz  and  the  reticulo-spinal  fas- 
ciculus; the  olfacto-mesencephalic  fasciculus  (Wallenberg) 
bears  fibers  directly  from  the  cortex  of  the  olfactory  tract  to  the 
tegmentum  of  the  mid-brain,  pons  and  medulla  and  on  into  the 
spinal  cord,  supposedly  to  genetic  nuclei.  Cerebellar  Connection. 
— The  connection  of  the  olfactory  nerve  with  the  cerebellum  is 
problematic.  Fibers  of  Wallenberg's  bundle  may  reach  the 
cerebellum;  it  is  known  that  certain  fibers  of  the  stria  medullaris 
thalami  go  beyond  the  nucleus  habenulse  to  the  tectum  of  the 
mid-brain,  especially  to  the  superior  colliculus;  and  nucleo- 
cerebellar  fibers  enter  the  cerebellum  as  tecto-cerebellar  tract, 
through  the  superior  medullary  velum.  Thus  olfactory  nuclei 
are  connected  with  the  cerebellar  cortex  and  coordinating  arcs 
are  completed  as  heretofore  described  (see  olfactory  projection 
and  association  neurones). 
24 


370  THE   RHOMBENCEPHALON 

Genetic  Nuclei  (Nn.  Origines)  (Fig.  133).^ — The  nuclei  of  the 
oculomotor,  trochlear,  abducent,  facial,  accessory  and  hypo- 
glossal nerves  and  the  nuclei  of  the  motor  roots  of  the  tri- 
geminal, glossopharyngeal  and  vagus  nerves  represent  the  an- 
terior columna  of  gray  matter  in  the  cord  and  constitute  the 
anterior  columna  series.  The  anterior  columna  and  center  of 
the  gray  crescent  in  the  spinal  cord  contain  two  functional 
columns  of  efferent  neurones,  somatic  and  visceral,  which  are  the 
counterpart  of  the  two  columns  of  afferent  neurones  in  the  pos- 
terior columna.  Though  the  gray  crescent  is  broken  up  in  the 
medulla  by  decussating  tracts  and  the  expansion  of  the  ven- 
tricle, all  four  columns  are  represented.  The  two  afferent 
columns  are  described  above;  they  form  the  somatic  and  visceral 
terminal  nuclei,  which  receive  the  axones  of  peripheral  afferent 
nerves.  Genetic  nuclei  originate  all  efferent  nerve  fibers;  and, 
since  they  supply  three  kinds  of  muscle  (besides  glands),  there 
are  three  kinds  of  genetic  nuclei,  one  somatic  and  two  visceral 
(Malone):  (i)  The  somatic  nuclei  of  origin  contain  large  cell- 
bodies  with  massive,  tigrous  cytoplasm;  they  supply  the  striated 
voluntary  muscles  of  the  body  {soma-  body).  (2)  The  common 
visceral  nuclei  of  origin  are  made  up  of  cell-bodies  which  are 
nearly  all  nuclei;  the  cytoplasm  is  so  scanty  that  the  nuclei 
are  relatively  very  large  and  the  narrow  rim  of  cytoplasm 
around  the  nucleus  presents  few  tigroid  bodies.  These  nuclei, 
through  sympathetic  ganglia,  innervate  the  smooth  involun- 
tary muscles  of  viscera  (and  gland-cells).  (3)  The  cardiac 
visceral  nuclei  of  origin,  through  sympathetic  ganglia,  innervate 
the  striated  involuntary  muscle  of  the  heart.  The  cell-bodies 
of  these  nuclei  are  intermediate  in  size  and  in  number  of  tigroid 
bodies  between  the  somatic  and  the  common  visceral  cells;  the 
rim  of  cytoplasm  is  broader  and  more  tigrous  than  in  the  com- 
mon visceral  neurone  but  not  nearly  equal  in  these  particulars 
to  the  somatic  neurones  (Fig.  134)  (Am.  Jour.  Anat.,  Vol.  15). 

The  cortical  connection  of  the  visceral  genetic  nuclei  has  not 
been  determined.  Such  connection  is  certainly  present,  but 
the  tracts  establishing  it  have  not  been  traced.  It  is  otherwise 
with  the  somatic  nuclei  of  origin.     These  nuclei  are  connected 


REFLEX   MECHANISMS  37 1 

with  the  cerebral  cortex  on  both  sides,  but  chiefly  with  that  of  the 
opposite  hemisphere.  The  connection  is  established  first  and 
principally  by  the  pyramidal  tracts,  some  of  the  fibers  running 
directly  from  the  tract  to  the  nucleus  and  others,  leaving  the 
tract  high  up,  run  through  the  accessory  fillet  (Bechterewi)  to  a 
point  near  the  respective  nuclei  which  they  are  about  to  enter; 
and,  second,  the  fronto-pontal,  temporo-pontal  and  intermediate 
paths  are  believed  to  send  some  fibers  to  the  genetic  nuclei  of 
the  same  side.  The  simple  reflex  connection  of  these  genetic 
nuclei  is  established  for  all  of  them  by  the  medial  longitudinal 
bundle;  by  the  anterior  tecto-spinal  bundle  and  by  the  olivary 
pedicle  (for  the  third,  fourth,  and  sixth),  by  the  trapezoid 
body  (for  the  seventh)  and  by  the  spinal  tract  of  the  trigeminal 
nerve  (for  the  fifth,  seventh,  and  twelfth).  The  coordinating 
reflex  mechanisms,  of  which  the  neurones  of  genetic  nuclei  form 
a  part,  are  made  up  (i)  of  the  afferent  paths  to  the  cerebellar 
cortex,  and  (2)  of  intermediate  links  between  cerebellar  cortex 
and  the  genetic  nuclei,  (i)  The  first  is  composed  of  afferent 
nerve-fibers  which  go  directly  to  the  cerebellum,  and  of  afferent 
nerves  and  nucleo-cerebellar  fibers,  which  rise  in  terminal  nuclei 
and  end  in  the  cerebellar  cortex.  (2)  The  intermediate  links 
are  two  or  three  in  number,  viz.,  the  Purkinje  neurones  to  cere- 
bellar nuclei  and  the  nuclear  neurones  which  comprise  the 
cerebello-tegmental  tracts  and  terminate  partly  in  genetic 
nuclei;  and,  again,  these  two  sets  of  neurones  together  with  one 
or  more  of  the  following  tracts — the  thalamo-spinal,  the  rubro- 
spinal, the  vestibulo-spinal,  and  the  medial  longitudinal  tracts. 


CHAPTER  V 
MEMBRANES  OF  THE  SPINAL  CORD 

(MENINGES  SPINALIS) 

Dura  Mater. — Through  the  foramen  magnum  the  membranes 
of  the  brain  are  continuous  with  those  of  the  cord  with  which 
they  are  very  similar  in  structure.  The  dura  mater  spinalis  is 
attached  to  the  margin  of  the  great  foramen  and  to  the  bodies 
of  the  first  two  or  three  cervical  vertebrae;  elsewhere,  though 
joined  to  the  vertebrae  by  fibrous  bands,  its  surface  is  free 
from  immediate  bony  attachment  and  it  does  not  possess  the 
periosteal  layer.  Thus  suspended,  it  hangs  as  an  open  sac, 
or  sheath  (Fig.  138)  and  reaches  down  to  the  third  sacral 
vertebra  where  it  is  constricted  to  a  fibrous  cord  which  blends 
with  the  periosteum  on  the  posterior  surface  of  the  coccyx. 
The  arachnoid  and  pia,  and  the  spinal  cord  and  cauda  equina 
are  contained  in  the  dural  sac  (Figs.  135,  136  and  138).  Ex- 
ternally, the  surface  of  the  dura  is  separated  from  the  wall  of 
the  spinal  canal  by  the  internal  vertebral  plexus  of  veins, 
areolar  tissue  and  fat.  The  outer  surface  is  composed  of  flat 
polygonal  cells,  like  the  inner  surface.  Its  internal,  serous 
surface  is  bathed  with  a  small  amount  of  cerebrospinal  fluid 
which  separates  it  from  the  arachnoid.  For  every  segment  of 
the  spinal  cord,  the  dura  presents,  on  either  side,  a  pair  of 
foramina,  through  which  run  the  anterior  and  posterior  roots 
of  the  spinal  nerves  (Fig.  135).  Those  nerve  roots  are  invested 
by  a  sheath  of  dura  prolonged  from  the  margins  of  the  foramina. 
The  dura  mater  of  the  cord  does  not  separate  into  two  lay- 
ers and  forms  neither  sinuses  nor  processes.  It  performs 
no  periosteal  function  and  possesses  no  arachnoid  granula- 
tions (pacchionian  bodies).  Its  two  surfaces  are  formed  by 
endothelium. 

372 


NEURONES   OF   GENETIC   I^TJCLEI 


373 


Arachnoid. — The  arachnoid  of  the  spinal  cord  {arachnoidea 
spinalis)  forms  a  sac  of  the  same  length  as  the  dural  sheath, 
with  which  it  is  externally  in  contact  (Figs.  135,  136  and  138).  It 
presents  two  serous  surfaces.  Internally,  bands  of  fibro-elastic 
tissue  attach  it  to  the  pia  mater  along  the  posterior  median  line 


^  Qk 


Fig.  134. — Three  forms  of  efferent  nuclear  neurones  as  described  and  pictured 
by  Edward  F.  Malone. 

I.  Is  from  the  nucleus  cardiacus  in  the  middle  of  the  nucleus  alae  cinerese.  2.  Is  from  that 
part  of  the  nucleus  alse  cinereae  which  supplies  smooth  muscle  and  glands.  3.  Is  from  hypo- 
glossal nucleus;  these  neurones  supply  striated  voluntary  muscle.  The  first  is  a  cardiac 
visceral  nucleus;  the  Second  a  common  visceral  nucleus;  and  the  third  a  somatic  nucleus. 
(Am.  Jour,  of  Anat.,  Vol.  iSt  and  Anat.  Rec,  Vol.  7.) 


of  the  cord  and  form  the  subarachnoid  septum  (Fig.  135).  The 
external  spinal  veins  and  a  considerable  space  separate  the  arach- 
noid from  the  pia  mater.  That  subarachnoid  space  is  filled 
with  fluid.  By  the  ligamenta  denticulata  it  is  divided  into  the 
anterior  and  posterior  subarachnoid  spaces,  which,  through  the 


374 


MEMBRANES    OF    THE    SPINAL   CORD 


foramen  magnum,  are  continuous  with  the  same  spaces  in  the 
cranial  cavity  (Figs.  6  and  135). 


Subarachnoid  septum 


Subarachnoid  trabecula 
with  bundles  of  poste- 
rior nerve-roots 


Ligamentum 
denticulatum 


Anterior  nerve-roots 
(in  sections) 


Subarachnoid  space 


Dura  mater 


Arachnoid 

Posterior  root 

Anterior  root 

Ligamentum  denticulatum 

Linea  splendens 


Dura  mater 


Fig.  135. — Meninges  of  the  spinal  cord.     A.  Transverse  section.     (After  Key 
and  Retzius.)     B.  Anterior  view.     (After  Ellis.     Morris's  Anatomy.) 

Lumbar  Puiicture. — For  diagnosis,  for  the  relief  of  pressure,  and  to  make 
room  for  subarachnoid  medication,  a  certain  amount  of  subarachnoid 
fluid  may  be  drawn  ofif  through  a  lumbar  puncture.    The  puncture  is  made 


CEREBRO-SPINAL   FLUID 


375 


either  between  the  third  and  fourth,  or  the  fourth  and  fifth  lumbar  arches; 
in  children  always  at  the  latter  location.  The  wide  separation  of  the  lumbar 
arches  affords  easiest  access  in  this  region,  and  puncture  below  the  fourth 
lumbar  vertebra  cannot  injure  the  cord.  The  normal  amount  of  cerebro- 
spinal fluid  is  100-130  cc,  of  which  20-30  cc.  are  usually  withdrawn  before 
introducing  such  medicinal  agents  as  neo-salvarsan  or  salvarsanized  serum 
in  the  treatment  of  syphilis. 

Pia  Mater. — The  pia  of  the  cord  {pia  mater  spinalis)  is  much 
stronger  than  that  of  the  brain  (Figs.  135  and  136).     It  has  two 


Ligamentum  denticulatum 


Interverte- 
bral foramen 


Body  of 
vertebra 
Periosteum 

Dura  mater 

Subdural 

space 

Arachnoid 

Subarachnoid 

space 

Pia  mater 


Fig.  136. — Diagrammatic  section  of  the  spinal  meninges  and  spinal  cord. 
(After  Morrises  Anatomy.) 

distinct  layers,  the  inner  of  which  is  continuous  with  the  brain 
pia  and  forms  an  epineurium  for  the  cord  and  roots  of  the  spinal 
nerves.  The  outer  is  the  more  vascular  layer.  Both  layers  dip 
into  the  anterior  median  fissure;  they  form  the  anterior  septum 
which  contains  the  anterior  spinal  artery.  The  inner  layer  is 
attached  to  the  septum  in  the  posterior  median  fissure.  The 
pia  mater  forms  the  linea  splendens  along  the  front  of  the  cord 
and  the  ligamentum  denticulatum  on  either  side.  The  denticu- 
late ligament  is  a  longitudinal  band  whose  straight  medial 
border  is  continuous  with  the  pia  along  the  middle  of  the  lateral 


376  MEMBRANES   OF    THE    SPINAL   CORD 

surface  of  the  cord;  its  lateral  border  is  notched  and  its  twenty 
teeth,  invested  with  arachnoid,  are  attached  to  the  dura  opposite 
the  first  twenty  vertebrae.  The  two  ligaments  subdivide  the 
space  between  the  pia  and  arachnoid  into  anterior  and  posterior 
subarachnoid  spaces.  A  filamentous  extension  of  the  pia, 
15  cm.  long,  helps  to  form  the  filum  terminale  internum.  It 
descends  in  the  arachno-dural  sheath  with  the  roots  of  the 
lumbar  and  sacral  nerves  and  all  together  constitute  the  cauda 
equina  (Fig.  138).  For  some  distance,  about  7.5  cm.,  the  filum 
terminale  internum  contains  gray  matter  and  rudimentary 
fibers  continuous  with  the  spinal  cord.  The  filum  unites  with 
the  arachnoid  and  dura  at  the  third  sacral  vertebra  in  forming 
the  filum  terminale  externum  which  forms  a  sort  of  ligament  for 
the  spinal  cord.  The  ligament  is  inserted  into  the  coccyx. 
The  pia  mater  of  the  cord  contains  the  trunks  and  large  branches 
of  the  anterior  and  the  two  posterior  spinal  arteries,  and  the 
tributaries  of  the  external  spinal  veins. 

Nerve  Supply. — The  membranes  of  the  spinal  cord  are  sup- 
plied by  recurrent  branches  of  the  spinal  nerves  and  by  the 
sympathetic.     The  recurrent  branches  are  sensory  in  function. 

BLOOD  SUPPLY  OF  THE  SPINAL  CORD 

The  vessels  supplying  the  cord  are  the  anterior  spinal  artery 
and  the  two  posterior  spinal  arteries  which  rise  at  the  foramen 
magnum  from  the  vertebral  arteries  and  are  reinforced  by 
cervical,  intercostal  and  lumbar  arteries.  The  anterior  spinal 
artery  {a.  spinalis  anterior)  descends  along  the  entrance  to  the 
anterior  median  fissure  (Fig.  137);  it  is  formed  by  the  union  of 
two  vessels,  one  from  each  vetebral.  The  posterior  Spinal 
artery  {a.  spinalis  posterior)  of  either  side,  is  in  reality  a  pair 
of  vessels  which  freely  communicate,  and  are  so  placed  as  to 
embrace  the  posterior  nerve  roots.  The  larger  vessel  of  the 
pair  is  anterior  to  the  nerve  roots,  while  the  smaller  is  between 
them  and  the  posterior  median  fissure  (Fig.  137).  The  spinal 
arteries  give  origin  to  two  sets  of  branches,  namely,  the  fissural 
or  centrifugal  and  the  centripetal  arteries.     Both  sets  are  end- 


SPINAL   ALTERIES 


377 


arteries  and  form  rich  longitudinal   plexuses   which  overlap 
each  other  but  do  not  anastomose. 

The  fissural  or  centrifugal  arteries  rise,  first  and  chiefly, 
from  the  anterior  spinal  artery  (Fig.  137).  These  enter  the 
anterior  median  fissure  and,  running  lateralward,  supply  the 
greater  part  of  the  gray  matter.  Second,  a  few  centrifugal 
arteries  rise  from  the  posterior  spinal  arteries.  Running  into 
the  posterior  fissure,  they  are  distributed  to  the  posterior  white 


I 

e  f    p  o       n 

Fig.  137. — The  arteries  and  veins  in  the  spinal  cord.  Diagrammatic. 
(After  Morrises  Anatomy.) 
a.  Dorsal  external  spinal  veins,  b.  Posterior  radicular  vein.  c.  Peripheral  venous 
plexus,  d.  Anterior  radicular  vein.  e.  Ventral  external  spinal  veins,  f .  Anterior  central 
vein.  g.  Posterior  central  artery  and  vein.  h.  Posterior  spinal  artery,  i.  Peripheral 
arterial  plexus,  j.  Posterior  radicular  artery,  k.  Intercostal  artery.  1.  Spinal  ramus. 
m.  Anterior  radicular  artery,  n.  Internal  spinal  vein.  o.  Anterior  central  artery,  p. 
Anterior  spinal  artery. 


columns,  the  posterior  commissure  and  to  the  nucleus  dorsalis 
(Clarki). 

The  centripetal  arteries  rise  from  both  the  anterior  and 
posterior  spinal  arteries  (Fig.  137).  They  enter  the  cord  at 
right  angles  to  the  surface  and  supply  the  white  matter  and 
the  peripheral  parts  of  the  gray  substance,  including  the  tips 
of  the  column ae.  Those  branches  to  the  columnae  accompany 
the  root-fibers. 


378  MEMBRANES    OF   THE    SPINAL   CORD 

Veins. — The  veins  that  carry  the  blood  from  the  interior  of 
the  cord,  the  venae  spinales  intemae,  are  the  fissural  veins,  which 
issue  from  the  fissures,  the  root-veins,  which  accompany  the  ante- 
rior and  posterior  root-fibers  to  the  surface  of  the  cord,  and  a 
small  number  of  veins  that  issue  from  other  parts  of  the  surface 
of  the  spinal  cord.  All  unite  in  forming  the  external  spinal 
plexus  (venae  spinales  extemae)  spread  over  the  entire  surface 
of  the  cord  beneath  the  arachnoid  membrane.  According  to 
Cunningham,  the  plexus  includes  six  longitudinal  veins — 
anterior  and  posterior  median  and,  on  either  side,  an  antero- 
lateral and  a  postero-lateral  vein  placed  just  behind  the  re- 
spective nerve  roots.  In  the  upper  cervical  region,  the  plexus 
forms  two  or  three  small  veins  which  empty  into  the  vertebral 
or  inferior  cerebellar  veins;  elsewhere,  by  a  branch  along  each 
spinal  nerve,  the  plexus  communicates  with  the  internal 
vertebral  plexus  (plexus  venosi  vertebrales  intemi)  outside 
the  dura  mater,  and  is  drained  into  the  vertebral,  intercostal, 
lumbar  and  sacral  veins.  No  valves  are  found  in  the  spinal 
veins. 

Lymphatics. — Perivascular  spaces  carry  the  lymph  from  the 
spinal  cord.  The  perineural  spaces  carry  a  centripetal  stream 
which  empties  into  the  lymph  spaces  of  the  cord  and  its  mem- 
branes (Orr  and  Rows :  Brain,  Vol.  3 6) .  There  are  no  lymphatic 
vessels  in  the  cord. 


CHAPTER  VI 
THE  SPINAL  CORD 

The  spinal  cord  {medulla  spinalis)  is  developed  from  the  pos- 
terior part  of  the  neural  tube,  and  forms  the  corresponding 
portion  of  the  central  axis  of  the  nervous  system. 

Extent. — It  is  continuous  with  the  medulla  oblongata,  above ; 
and,  in  the  adult,  reaches  to  the  lower  border  of  the  first  lumbar 
vertebra  (Fig.  138).  Its  length  is  43-45  cm.  (17-18  in.).  In 
a  very  slender  process  the  filum  terminale  internum,  the  cord 
is  continued  beyond  the  first  lumbar  vertebra.  That  process 
and  the  lower  spinal  nerves  form  the  cauda  equina  which  is 
inclosed  in  a  sheath  composed  of  the  arachnoid  and  dura  mater. 
The  filum  terminale  internum  for  about  7.5  cm.  contains  a 
prolongation  of  the  central  gray  matter  and  ventricle  of  the 
cord  and  also  a  few  fibers  which  suggest  the  coccygeal  nerves 
of  lower  animals. 

In  the  foetus  before  the  third  month,  the  cord  and  spinal 
canal  are  of  equal  length.  It  touches  the  base  of  the  sacrum  at 
the  sixth  month  in  utero.  At  birth  the  cord  reaches  the  third 
lumbar  vertebra  and  it  continues  to  recede  with  the  rapid 
growth  of  the  vertebrae  to  its  adult  position. 

Diameters  (Fig.  139). — The  spinal  cord  is  shaped  Hke  a 
cylinder,  slightly  flattened  from  before  backward  (dorso-ven- 
trally).  Its  longest  diameter  is  transverse  and  measures  less 
than  12  mm.  (0.5  in.),  except  in  the  cervical  and  lumbar  en- 
largements of  the  cord.  In  the  latter  it  equals  12-13  i^^^- 
and  in  the  former  15  mm.  (0.6  in.).  The  thoracic  portion  of 
the  cord  is  small  and  nearly  cylindrical  in  shape.  Divested 
of  its  meninges  and  nerves  the  spinal  cord  weighs  about  28 
grams  or  one  ounce  avoirdupois. 

Though  the  post-natal  growth  of  the  spinal  cord  lags  behind 
that  of  the  vertebral  column,  its  growth  is  relatively  greater 

379 


38o 


THE    SPINAL   CORD 


after  birth  than  that  of  the  brain:  the  brain  a  little  more  than 
triples  its  weight  at  birth;  by  extrauterine  growth,  the  weight 
of  the  cord  increases  seven  fold. 

The   cervical  enlargement   {intumescentia  cervicalis)    extends 


Superior  or  Cervical  Segment 
of  Spinal  Cord. 


Middle  or  Dorsal  Portion 
of  Cord. 


Inferior  Portion  of  Cord  and 
Cauda  Equina. 


Fig.  138. — Posterior  view  of  the  spinal  cord,  the  dura  mater  and  the  arachnoid 
being  laid  open  and  turned  aside.     (Brubaker  after  Sappey.) 

I.  Floor  of  fourth  ventricle.  2.  Brachium  conjunctivum.  3.  Brachium  pontis.  4. 
Restiform  body.  5.  Clava.  6.  Glossopharyngeal  nerve.  T.  Vagus.  8.  Accessory  nerve. 
9»  9.  9i  9'  Ligamentum  denticulatum.  10,  lo,  10,  10.  Posterior  roots  of  spinal  nerves. 
II,  II,  II,  II.  Posterior  lateral  sulcus.  12,  12,  12, 12.  Spinal  ganglia.  13,  13.  Anterior  roots 
of  spinal  nerves.  14.  Anterior  and  posterior  divisions  of  spinal  nerve.  15.  Conus  medul- 
laris.  16,  16.  Filum  terminales  internum.  17,  17.  Cauda  equina.  I-VIII.  Cervical 
nerves.     I-XII.  Thoracic  nerves.     I-V.  Lumbar  nerves.     I-V.  Sacral  nerves. 


from  the  medulla  oblongata  to  the  second  thoracic  vertebra 
(Figs.  138  and  139).  Its  greatest  diameter  is  on  a  level  with  the 
fifth  intervertebral  disc.  It  gives  origin  to  the  motor  fibers  and 
receives  the  sensory  fibers  of  the  nerves  which  form  the  cervical 
and  brachial  plexuses. 


SECTIONS   OF   SPINAL   CORD 

Post,  median  sept. 
Postero-lat.  sul.  ?•  I-  F-  I         F""^^'  intermediate  furrow 


381 


Pormatio  reticularis 
Anterior  root  line 


Sixth  ventricle 


^Jb 


,  Gelatinous  substance 


Fig.  139. — Sections  of  the  spinal  cord:  A.  The  cervical.     B.  The  thoracic    C. 

The  lumbar,  and  D.  the  sacral.     Unstained.     (Original.) 

A.  Section  of  ceri  veal /cord.     A.  C.  Anterior  columna,  P.  C.  Posterior  columna,  C.  G. 

Gray  commissure,   anterior   gray   and   posterior.     Com.   A.  White   anterior  commissure. 

Fun.    Ant.  Funiculus    anterior.    Fun.     Lat.  Funiculus    lateralis.     Fun.    Post.  Funiculus 

Eosterior.     G.  Fasciculus  gracilis.     C.  Fasciculus  cuneatus.     B.  Section  of  thoracic  cord. 
.  C.  Lateral  columna.     C.  Section  lumbar  cord.     D.  Section  of  lower  sacral  cord. 


382  THE   SPINAL   CORD 

The  lumbar  enlargement  {intumescentia  lumhalis)  begins  at 
the  tenth  thoracic  vertebra  and  increases  to  the  twelfth  (Figs. 
138  and  139).  Opposite  the  first  lumbar  vertebra  it  tapers  off 
almost  to  a  point,  the  conus  medullaris,  but  a  very  small  process 
continues  in  the  filum  terminale  internum.  From  the  lumbar 
enlargement  rise  the  motor  fibers  of  the  nerves  contained  in  the 
lumbar  and  sacral  plexuses,  and  into  it  enter  the  sensory  fibers 
of  the  same  plexuses. 

Ventricle  (Fig.  139,  B). — The  central  canal  of  the  spinal 
cord  {canalis  centralis  spinalis)  is  the  representative  of  the 
cavity  of  the  neural  tube.  It  is  just  visible  to  the  naked  eye, 
but  it  extends  throughout  the  cord  and  expands  above  into 
the  fourth  ventricle.  In  the  conus  medullaris  it  is  also  dilated, 
forming  the  ventriculus  terminalis  (Krausei).  It  is  lined  with 
columnar  ciliated  cells  which  stand  on  a  thick  lamina  of  sub- 
stantia gelatinosa. 

Fissures  of  the  Spinal  Cord  (Fig.  139). — The  spinal  cord 
is  incompletely  divided  into  symmetrical  lateral  halves  by  the 
anterior  and  the  posterior  median  fissure. 

The  anterior  median  fissure  (fissura  mediana  anterior)  is 
the  broader  and  shallower  of  the  two  (Fig.  139).  It  extends  in 
length  from  the  inferior  end  of  the  ventral  surface  of  the  pons 
(foramen  caecum  of  Vicq  d'Azyr)  down  the  anterior  median  line 
of  the  medulla  and  cord.  As  to  depth,  it  equals  one-third  of  the 
cord's  axis.  Its  floor  is  formed  by  the  white  anterior  com- 
missure. Both  layers  of  pia  mater  dip  down  into  it  and  inclose 
the  anterior  spinal  artery  and  its  branches.  The  anterior 
median  fissure  is  interrupted  at  the  junction  of  the  cord  and 
medulla  by  the  decussation  of  the  pyramids.  In  the  lumbar 
enlargement  it  gradually  disappears. 

The  posterior  median  fissure  {fissura  mediana  posterior) 
is  narrow  and  deep  (Fig.  139).  It  extends,  longitudinally,  down 
the  posterior  median  line  of  the  cord  from  the  middle  of  the 
posterior  surface  of  the  medulla.  It  divides  the  cord,  dorso- 
ventrally,  beyond  its  middle.  The  floor  of  the  fissure  is  formed 
by  the  posterior  commissure,  which,  with  the  gray  and  white 
anterior  commissures,  separates  the  posterior  from  the  anterior 


CERVICAL   AND    THORACIC   CORD 


3^3 


median  fissure.  The  posterior  mediam  fissure  is  not  an  open 
fissure;  it  is  occupied  by  a  lamina  of  connective  tissue,  the 
posterior  septum,  which  is  attached  to  the  deep  layer  of  the  pia 


Fasciculus  cuneatus 


Fasciculus 
gracilis  Posterior  septum 


Dorsal  (posterior) 
root 

Dorsal  (pos- 
terior) horn 


Lateral  horn 
Ventral  (anterior) 
horn 
Ventral  (anterior)  horn 


Nucleus  dorsalis 


Fig.  140. — Stained  sections  of  cervical  and  thoracic  cord.     (From  Morris.) 

mater.  In  the  posterior  septum  ramify  branches  of  the  two 
posterior  spinal  arteries  and  tributaries  of  the  external  spinal 
veins. 


384 


THE   SPINAL   CORD 


Fig.  141. — Stained  sections  of  lumbar,  sacral  and  coccygeal  cord.    (From  Morris.) 


SULCI   OF    SPINAL   CORD 


385 


25 


386 


THE   SPINAL   CORD 


Posterior  Lateral  Sulcus  (s.  lateralis  posterior). — Each  lateral 
half  of  the  spinal  cord  is  partially  divided  near  the  junction  of 
the  posterior  fourth  with  the  anterior  three-fourths  of  its  semi- 


^-^^J; 
:^+^  (u-^ 

o^  « 


circumference  by  the  posterior  lateral  sulcus  (Fig.  139).  The 
sulcus  is  situated  opposite  the  posterior  columna  of  gray  matter, 
to  which  it  transmits  the  posterior  roots  of  the  spinal  nerves.  It 
is  continuous  above  with  the  posterior  lateral  sulcus  of  the 


INTERMEDIATE   SULCI  387 

medulla.  It  separates  the  posterior  surface  and  the  antero- 
lateral surface  from  each  other. 

Anterior  Root-line  (s.  lateralis  anterior). — As  a  landmark, 
it  is  convenient  to  call  the  longitudinal  line  through  which  issue 
the  most  lateral  fibers  of  the  anterior  roots  of  the  spinal  nerves, 
the  anterior  root-line  of  the  spinal  cord  (Fig.  139).  There  is  no 
groove  on  the  surface  of  the  cord  along  this  line  and  it  is  mis- 
leading to  call  it  a  sulcus,  as  has  been  the  custom.  It  is  situated 
opposite  the  anterior  columna  of  gray  matter  and  in  line  with 
the  anterior-lateral  groove  of  the  medulla  oblongata.  Through 
it  and  through  the  surface,  just  medial  to  it,  emerge  the  anterior 
roots  of  the  spinal  nerves.  It  subdivides  the  antero-lateral 
surface  into  anterior  and  lateral  surfaces. 

The  posterior  intermediate  sulcus  (s.  intermedius  posterior) 
is  a  slight  longitudinal  groove  in  the  cord  which  subdivides  the 
upper  three-fourths  of  the  posterior  surface  into  postero-medial 
surface  and  postero-lateral  surface  (Fig.  139).  From  it  a  con- 
nective-tissue septum  extends  into  the  cord  and  separates  the 
fasciculus  gracilis  and  fasciculus  cuneatus  from  each  other. 
The  posterior  intermediate  furrow  is  found  only  in  the  medulla 
and  in  the  cervical  and  upper  eight  thoracic  segments  of  the 
cord. 

Sulcus  Intermedius  Anterior. — Rarely  an  anterior  inter- 
mediate sulcus  is  found  along  the  lateral  border  of  the  anterior 
pyramidal  tract.     It  was  described  by  Rauber. 

GRAY  MATTER  OF  THE  CORD 

The  spinal  cord  is  composed  of  (i)  gray  matter  {substantia 
grisea  spinalis),  in  the  central  part;  and  (2)  white  matter  (sub- 
stantia alba  spinalis)  in  the  peripheral  area.  It  is  like  the 
medulla  and  pons  in  having  the  white  matter  on  the  surface 
(Fig.  139). 

A  column  of  gray  matter  (Fig.  139),  crescentic  in  section, 
extends  through  the  center  of  each  lateral  half  of  the  spinal  cord. 
The  crescent  is  conyex  medially  and  is  joined  to  its  fellow  a 
little  in  front  of  the  middle  by  a  vertical  transverse  lamina  of 
gray  matter  called  the  gray  commissure   (commissura  grisea). 


388  THE    SPINAL   CORD 

It  is  joined  to  the  white  matter  of  the  opposite  side  by  the  white 
anterior  commissure.  The  points  of  the  crescent  are  directed 
forward  and  backward,  respectively,  and  form  the  anterior  and 
posterior  columnce.  A  lateral  projection  from  the  center  of  the 
crescent,  visible  only  in  the  thoracic  region,  is  called  the  lateral 
columna;  it  fuses  with  the  anterior  columna  in  the  cervical  and 
lumbar  enlargements.  Together  the  two  crescents  and  the 
gray  commissure  form  an  H-shaped  column  of  gray  matter. 
The  H-shaped  column  is  well  marked  in  the  cervical  and 
thoracic  regions  but  toward  the  lower  end  of  the  cord  the 
crescents  become  short  and  thick,  and  the  gray  column  is 
a  fluted  cylinder. 

The  H-shaped  colunin  is  composed  of  two  kinds  of  gray  sub- 
stance ^  viz. :  (i)  The  substantia  gelatinosa  (Rolandi),  which  forms 
(a)  a  cap  for  the  head  of  the  posterior  columna  and  (b)  an  en- 
velope for  the  central  canal,  or  ventricle,  of  the  cord.  (2)  The 
substantia  spongiosa.  The  latter  forms  all  the  H-shaped  column 
except  the  tips  of  the  posterior  columnae  and  the  thick  sheath  of 
the  central  canal.  Imbedded  in  the  neuroglia  there  is  a  net- 
work of  medullated  nerve  fibers  and  these,  with  the  common 
stains,  give  rise  to  a  spongy  appearance  under  the  microscope. 

Gray  Crescent  (Fig.  140). — It  is  made  up  of  (i)  the  anterior 
columna;  (2)  the  center,  which  is  joined  to  its  fellow  of  the 
opposite  side  by  the  gray  commissure  and  which  forms  the 
lateral  projection,  called  the  lateral  columna;  and  (3)  the 
posterior  columna.  The  lateral  border  of  the  crescent  is  not 
everywhere  clear  cut  and  definite,  especially  in  the  cervical 
region,  but  is  intermingled  for  a  short  distance  with  the  white 
matter,  forming  the  formatio  reticularis.  The  formatio  reticu- 
laris is  found  in  the  cervical  region,  elsewhere  it  is  very  feebly 
developed. 

It  is  well  to  keep  in  mind  the  four  functional  columns  that 
comprise  the  gray  substance  of  the  primitive  cord.  They  are 
definitely  represented  in  the  human  cord  and  their  arrangement 
is  as  follows  from  before  backward:  somatic  efferent  (voluntary 
motor)  in  the  anterior  columna;  visceral  efferent  (involuntary 
motor  and  glandular)  in  the  lateral  columna;  visceral  afferent 


CELLS  OF  ANTERIOR  COLUMNA  389 

(non-sensory,  exci to-reflex)  in  the  dorsal  nucleus  of  Clark;  and 
somatic  afferent  (sensory)  in  the  posterior  columna. 

I.  The  anterior  coltimna  (columna  anterior)  (Fig.  140)  as 
seen  in  sections  is  short  and  thick  compared  with  the  posterior 
columna.  It  is  thickest  in  the  cervical  and  lumbar  enlarge- 
ments, where  it  swells  out  sharply  toward  the  lateral  surface  of 
the  cord;  in  the  mid- thoracic  region  it  is  more  slender.  It 
does  not  reach  the  surface  of  the  cord.  It  ends  in  a  bulbous, 
serrated  head,  which  points  toward  the  anterior  root-line,  and 
is  joined  to  the  center  of  the  crescent  by  the  cervix  or  base. 
From  it  the  anterior  roots  of  the  spinal  nerves  rise;  and,  together 
with  the  anterior  root-fibers,  it  separates  from  each  other  the 
anterior  and  lateral  white  columns  of  the  cord. 

Cells  of  the  Anterior  Columna  (Figs.  142  and  143). — The  gray 
matter  of  the  spinal  cord  contains  multipolar  neurones  of  the 
Golgi  and  Deiters  types.  The  Golgi  cells  ramify  richly  in  the 
gray  matter  about  the  cell-bodies  and  both  their  axones  and 
dendrites  terminate  in  relation  with  other  neurones  in  the  adja- 
cent gray  substance.  The  long  axones  of  the  Deiters  cells  either 
enter  into  the  anterior  roots  (radices  anterior)  and  the  neurones 
are  called  radicular  cells  or  they  enter  into  a  longitudinal  tract 
or  fasciculus  and  the  neurones  are  na,m.ed  fascicular  cells.  The 
dendrites  of  the  Deiters  cells  arborize  in  both  the  gray  and 
white  substance.  The  axones  of  the  fascicular  cells  form,  first, 
certain  ascending  tracts  of  the  anterior  and  lateral  funiculi;  and 
second,  dividing  T-like  into  ascending  and  descending  rami, 
they  form  the  anterior  and  much  of  the  lateral  fasciculus  pro- 
prius.  The  bodies  of  the  radicular  cells  in  the  anterior  columna 
are  large  and  vesicular  in  character.  They  are  motor  in 
function  and  their  axones  form,  in  great  part,  the  anterior  roots 
of  the  spinal  nerves.  They  constitute,  therefore,  the  genetic 
nuclei  of  spinal  nerves.  Because  they  supply  striated  voluntary 
muscles  they  are  somatic  genetic  nuclei.  Together  with  the 
neurones  of  the  genetic  nuclei  of  cerebral  nerves  these  of  the 
anterior  columna  constitute  the  lower  segment  motor  neurones. 

Two  chief  columns  of  cell-bodies  are  located  in  the  anterior 
columna,  the  medial  coltimn  and  the  lateral  column  (Figs. 


390  THE   SPINAL   CORD 

142  and  143).  The  former  is  continuous  throughout  the  cord 
with  the  exception  of  the  fifth  lumbar,  the  first  and  fifth  sacral 
and  the  coccygeal  segments,  while  the  lateral  column  is  found 
only  in  the  cervical  and  lumbar  enlargements.  The  medial 
column  of  cells  shows  a  double  group  in  sections  of  the  lower 
three  cervical,  all  the  thoracic  and  the  first  lumbar  segments  of 
the  cord.  These  subgroups  are  called  the  ventro-medial  and 
the  dor  so-medial  cells.  Only  the  ventro-medial  group  is  present 
above  the  sixth  cervical  segment  and  below  the  first  lumbar 
segment.  The  dendrites  of  the  cell-bodies  in  the  medial 
column  arborize  in  the  gray  substance  of  the  same  columna, 
in  the  adjacent  white  matter  of  the  anterior  column  of 
the  cord  and,  to  some  extent,  in  the  opposite  anterior  col- 
umna, having  passed  through  the  white  anterior  commissure; 
the  axones  of  these  medial  cell-bodies  enter  very  largely  into 
the  anterior  roots  of  the  spinal  nerves  on  the  same  side ;  but  a 
certain  number  probably  run  through  the  white  anterior  com- 
missure into  the  anterior  nerve-roots  of  the  opposite  side,  and 
others  enter  into  the  fasciculi  proprii  of  the  cord. 

The  lateral  column  of  cells  in  the  anterior  columna  is  a  large 
one  (Figs.  142  and  143).  It  is  found  only  in  the  regions  which 
innervate  the  extremities,  that  is,  in  the  cervical  and  lumbar 
enlargements.  It  is  everywhere  divided  into  a  ventro-lateral 
and  a  dorso-lateral  cell-group ,  and  in  most  of  the  segments  of  the 
lumbar  enlargement  there  are  two  other  cell-groups,  according 
to  Alexander  Bruce.  One  of  them  is  located  behind  the  dorso- 
lateral cells  and  is  called  the  post-dor  so-lateral  group;  and  the 
other,  which  occupies  the  angle  between  the  ventro-lateral  and 
the  dorso-lateral  cells,  lying  medial  to  both,  is  called  the  central 
group  (Cunningham).  The  dendrites  of  the  cell-bodies  in  the 
lateral  column  arborize  and  end  both  in  the  gray  matter  of  the 
anterior  columna  and  in  the  white  matter  adjacent  to  its 
lateral  surface;  the  axones  proceed  largely  into  the  anterior 
roots  of  the  spinal  nerves  but  partly  into  the  longitudinal 
white  columns  of  the  cord.  Probably  the  medial  column 
innervates  the  trunk  muscles;  the  lateral  column,  the  muscles 
of  the  extremities. 


SECTION  OF   LUMBAR  CORD 


391 


According  to  Bruce,  a  baso-lateral  group  of  cell-bodies  in  the 
anterior  columna,  found  in  the  first  six  cervical  segments,  forms 


the  genetic  nucleus  of  the  spinal  root  of  the  accessory  nerve;  and 
the  central  group,  in  the  fourth  and  fifth  segments  and  the 


392 


THE    SPINAL   CORD 


adjacent  parts  of  the  third  and  sixth  segments,  is  the  nucleus 
from  which  the  phrenic  nerve  originates. 


Cortical  Connection. — The  cells  of  the  anterior  columna  are 
brought  into  relation  with  the  anterior  (direct)  pyramidal 
fibers^and  the  lateral  (crossed)  pyramidal  fibers  by  means  of 


REFLEX  MECHANISMS  393 

intermediate  neurones.  In  this  manner  motor  and  inhibitory 
impulses  descend  to  them  from  the  cerebral  cortex,  coming  from 
the  opposite  hemisphere,  chiefly,  but  also  from  the  same  side. 
It  has  been  the  belief  that  the  end-tufts  of  the  fibers  in  the 
anterior  and  lateral  pyramidal  tracts  are  in  direct  contact  with 
the  dendrites  or  cell-bodies  of  the  neurones  in  the  anterior 
columna;  but  the  investigations  of  Schafer,  Collier  and  others, 
indicate  that  this  connection  between  the  neurones  of  the 
anterior  columna  and  the  lateral  pyramidal  fibers,  at  least,  is 
established  by  intervening  neurones  whose  cell-bodies  are 
located  near  the  base  of  the  posterior  columna  in  the  region 
of  the  nucleus  dorsalis  (Clark's  column) .  The  evidence  of  such 
termination  of  the  anterior  pyramidal  tract  is  not  conclusive. 
The  anterior  columna  cells  also  are  in  relation  with  the  end- 
tufts  of  posterior  root-fibers  and  with  axones  whose  cell-bodies 
are  located  in  the  center  and  posterior  columna  of  the  gray 
crescent.  The  latter  neurones  form  contact  relations  with 
fibers  of  the  posterior  roots  of  the  spinal  nerves  on  both  sides. 
Thus  both  by  immediate  contact  between  anterior  and  posterior 
root-neurones  and  by  the  intervention  of  an  intrinsic  spinal 
neurone  the  simple  reflex  mechanism  of  the  spinal  cord  is 
formed. 

More  extensive  simple  reflex  connections  are  established  by 
the  fasciculi  proprii,  which  are  analogous  to  the  medial  longi- 
tudinal bundle  in  the  brain-stem.  The  coordinating  reflex 
mechanism  to  which  the  neurones  of  the  anterior  columna  be- 
long is  made  up  (i)  on  its  afferent  side  of  the  sensory  fibers 
of  spinal  nerves,  the  spino-cerebellar  tracts  and  the  arcuate 
fibers  of  the  medulla,  etc. ;  (2)  on  its  efferent  side  of  the  Purkinje 
neurones,  the  cerebello-tegmental  tracts  and  three  tracts  which 
connect  with  the  anterior  columna,  viz.,  the  thalamo-spinal, 
rubro-spinal  and  vestibulo-spinal  tracts. 

Lesions. — Paralysis  due  to  lesions  of  the  anterior  columna 
and  of  the  genetic  nuclei  of  cerebral  nerves  is  often  called  lower 
segment  paralysis.  It  is  characterized  by  flaccidity  and  ab- 
sence of  reflexes.  The  cells  in  the  anterior  columna  are  the  seat 
of  hemorrhagic  inflammation  and  rapidly  degenerate  in  acute 


394  THE    SPINAL   CORD 

anterior  poliomyelitis.  In  progressive  muscular  atrophy  and 
in  amyotrophic  lateral  sclerosis  they  degenerate  slowly.  As  a 
result  of  the  first,  sudden  flaccid  paralysis  occurs.  The  muscles 
waste  away  in  the  second  and  third  because  the  nerves  control- 
ling the  muscles  and  their  blood  supply  are  gradually  destroyed. 
In  the  last,  the  muscles  are  also  spastic,  because  the  involvement 
of  the  pyramidal  tracts  cuts  off  cerebral  inhibition. 

2.  Center  of  Crescent  and  Colnmna  Lateralis  (Fig.  140). — 
In  the  center  of  the  crescent  there  are  many  small,  closely 
packed  cell-bodies,  belonging  to  types  one  and  two.  The  type 
two  cells  (Golgi's)  are  locally  associative  within  the  same  seg- 
ment. The  first  type  cells  (DeitersO  are  either  associative 
(fascicular)  or  radicular.  A  few  of  the  associative  cells  send 
their  axones  through  the  anterior  commissure  to  the  opposite 
crescent;  they  are  commissural  in  function.  The  greater  number 
of  these  associative  cells  send  their  axones  into  the  lateral 
column,  where  they  divide  T-like  into  ascending  and  descend- 
ing rami  and  establish  connections  with  segments  above  and 
below  the  point  of  origin.  There  are  also  a  number  of  non- 
chromophilous  cells  in  the  center  of  the  crescent,  concerning 
which  we  have  no  detailed  information.  Exclusive  of  these  non- 
chromophilous  cells,  there  are  two  distinct  cell-columns  in  the 
central  part  of  the  crescent,  viz.,  the  intermedio-lateral  column 
(lateral  intermediate) ,  and  the  deep  intermediate  column  (middle 
column  of  Waldeyer) .  The  former  contains  radicular  neurones; 
the  latter,  chiefly,  fascicular  neurones. 

Deep  Intermediate  Column. — This  column  of  medium-sized 
cell-bodies  extends  through  the  cord  in  the  medial  part  of  the 
crescent,  adjacent  to  the  gray  commissure.  The  cells  possess 
long  dendrites  which  arborize  dorsalward,  among  the  in-coming 
posterior  root-fibers;  the  axones  in  small  part  run  through  the 
anterior  commissure  to  the  opposite  crescent;  the  greater  number 
proceed  lateralward  and,  by  their  T-branches,  form  the  deepest 
part  of  the  lateral  fasciculus  proprius.  The  primary  axone  and 
both  its  T-branches  give  off  collaterals  which  terminate  at 
various  levels  and  increase  the  scope  of  the  association. 

The  intermedio-lateral  column  of  cell-bodies  (Fig.  142,  B)  is 


A  VISCERAL  NUCLEUS   OF   ORIGIN  395 

a  visceral  genetic  nucleus  found  in  the  center  of  the  crescent.  In 
the  thoracic  segments  of  the  cord,  where  the  lateral  columna  is 
visible,  this  column  is  contained  in  the  lateral  columna  and  in 
the  white  matter  immediately  adjacent  to  it;  so  far  as  it  is  found 
in  the  cervical  and  lumbar  enlargements  it  is  situated  in  the  base 
of  the  anterior  columna  near  its  lateral  surface.  The  intermedio- 
lateral  column  is  found  in  the  last  cervical,  all  the  thoracic  and 
the  first  and  second  lumbar  segments,  in  a  nearly  continuous 
column;  it  is  also  found  in  the  third  and  fourth  sacral  segments 
of  the  cord  and  in  the  first  four  cervical  (Cunningham).  The 
first  region  (from  last  cervical  to  second  lumbar  segment) 
corresponds  in  position  and  extent  to  the  origins  of  the  white 
rami  communicantes;  the  second  region  is  at  the  level  of  origin 
of  the  pelvic  splanchnics;  and  the  cell-groups  representing  this 
column  in  the  upper  cervical  segments  probably  contribute 
sympathetic  fibers  to  the  accessory  and  phrenic  nerves. 

The  cells  of  the  intermedio-lateral  column  are  largely  of  the 
radicular  variety,  their  slender  axones  enter  into  the  anterior 
roots  of  the  spinal  nerves.  Whether  any  belong  to  the  strand- 
variety  is  not  known.  They  are  in  contact  relation  with  posterior 
root-fibers  and  are  also  connected  with  the  posterior  roots  by 
intervening  neurones.  Their  cerebral  connection  has  not  been 
traced.  They  are  sympathetic  or  autonomic  in  function. 
The  intermedio-lateral  column  is  the  visceral  eferent  column  oj 
neurones  found  in  animals  having  the  tubal  t)^e  of  nervous 
system;  it  is  destined  to  supply  involuntary  muscle  and  glands. 
Within  it  are  the  automatic  spinal  centers,  such  as,  the  cilio- 
spinal,  cardiac-accelerator,  vaso-motor,  secretory,  trophic, 
inhibito-secretory,  viscero-motor,  viscero-inhibitory,  etc.  That 
the  cell-bodies  in  the  center  of  the  crescent  are  of  sympathetic 
junction  is  suggested  by  two  facts:  first,  the  cell-bodies  are 
small,  which  indicates  that  the  axones  run  but  a  short  distance 
from  the  neurone  center,  as  is  the  case  with  spinal  sympathetic 
neurones;  and,  second,  the  distribution  of  these  central  neurones 
is  limited  to  those  regions  of  the  spinal  cord  whence  the  efferent 
sympathetic  fibers  rise. 

3.  The  posterior  columna  {columna  posterior)  except  in  the 


396  THE    SPINAL   CORD 

lower  cord,  is  slender  (Fig.  140).  It  is  longer  than  the  anterior 
columna  and  reaches  the  surface  in  the  posterior  lateral  sulcus, 
where  it  receives  the  posterior  roots  of  the  spinal  nerves.  The 
posterior  columna  presents  a  slight  enlargement  near  its 
extremity,  called  the  caput  columncB,  which  tapers  off  to  the 
apex  columncB.  The  head  is  joined  to  the  base  by  a.  constricted 
part,  the  cervix.  The  head  of  the  posterior  columna  is  capped 
by  a  V-shaped  mass  of  substantia  gelatinosa.  Spongy  substance 
makes  up  the  remainder  of  it.  The  posterior  columna  separates 
the  posterior  from  the  lateral  column  of  the  cord  (Figs.  142 
and  143). 

The  substantia  gelatinosa  of  the  posterior  columna  is  often 
crescentic  in  shape.  It  forms  a  characteristic  feature  of  the 
gray  matter  of  the  cord  and  a  prominent  nucleus  (of  the  tri- 
geminal nerve)  in  the  medulla  and  pons.  It  is  made  up  of  two 
layers:  (i)  The  stratum  zonale,  a  dense  plexus  of  fine  fibers 
entering  it  from  Lissauer^s  tract,  most  of  them  non-medul- 
lated,  and  (2)  a  clear  zone,  the  gelatinous  substance  proper, 
containing  a  loose  plexus  of  non-medullated  fibers,  packed  with 
small,  multipolar  cell-bodies,  which  possess  very  unstable 
cytoplasm.  Deeply,  the  gelatinous  substance  is  limited  and 
separated  from  the  nucleus  of  the  posterior  columna  by  a  second 
dense  plexus  of  non-medullated,  longitudinal  fibers,  called  by 
KoUiker  the  plexus  of  the  gellatinous  substance  (Ranson:  Am. 
Jour.  Anat.,  Vol.  16). 

The  cells  of  the  posterior  columna  are  numerous  and  of  both 
types.  In  the  head  of  the  posterior  columna  they  have  smaller 
bodies  (10  n)  than  the  cells  of  the  columna  anterior.  They  are 
less  definitely  grouped  and  are  fusiform  or  stellate  in  shape 
throughout  the  caput  columnae;  but  in  the  base  of  the  horn, 
near  its  medial  surface,  they  have  large  vesicular  bodies 
(40-100  11)  and  form  one  of  the  most  definite  cell-columns  in  the 
spinal  cord.  The  cells  may  be  grouped  as  follows:  (i)  the 
apical  cells  in  the  gelatinous  substance;  (2)  the  central  cells  of 
the  caput  columnae,  the  nucleus  of  the  posterior  column;  (3)  the 
baso-lateral  cells,  which  extend  out  into  the  formatio  reticularis; 
and  (4)  the  baso-medial  cells,  which  form  the  dorsal  nucleus  of 


SOMATIC   TERMINAL   NUCLEUS 


397 


Clark.  All  these  neurones  are  somatic  afferent  in  Junction 
(common  sensory)  except  two  groups — the  baso-medial  group, 
which  is  visceral  afferent,  and  the  baso-lateral  group  which  is 
intercalated  between  the  pyramidal  tract  and  the  radicular  neurones 
of  the  anterior  column.  The  dendrites  of  the  posterior  column 
neurones  ramify  within  the  gray  substance  toward  the  apex 
of^the  column,  forming  contacts  with  the  posterior  root-fibers. 
The  axones  either  enter  the  longitudinal  fasciculi  of  the  cord 
or  proceed  to  some  more  anterior  part  of  the  gray  substance. 


Fig.  146. — Transverse  sections  through  the  spinal  cords  of  embryos  of  {A) 

about  four  and  a  half  weeks  and  {B)  about  three  months. 

cB,  Fasciculus  of  Burdach;  cG,  fasciculus  of  Goll;  dh,  dorsal  column;  dz,  dorsal  zone;  fp, 

fioor-plate;  ob,  oval  bundle;  rb,  roof-plate;  vh,  ventral  column;  vz,  ventral  zone.    (His.) 

Those  of  the  dorsal  nucleus  form  the  dorsal  spino-cerebellar  tract. 
The  axones  of  the  gelatinous  neurones  and  of  a  few  large  cells 
in  the  caput  columnae  adjacent  to  the  gelatinous  substance,  enter 
the  lateral  fasciculus  proprius  and,  dividing  into  cephalic  and 
caudal  branches,  form  the  association  bundle  of  the  dorsal  horn 
(Cajal).  A  number  of  axones  from  other  parts  of  the  posterior 
columna  enter  the  lateral  fasciculus  proprius  and,  also,  the 
posterior  fasciculus  proprius;  they  bifurcate  in  the  usual  way  and 
establish  connections  with  a  variable  number  of  segments  above 


398 


THE    SPINAL   CORD 


and  below  their  points  of  origin.  The  greater  number  of  pos- 
terior column  neurones  send  their  axones  forward  either  to  the 
center  or  anterior  column  of  the  same  crescent  or,  by  way  of  the 
gray  and  white  commissures,  to  the  center  and  anterior  column 
of  the  opposite  crescent.  This  large  group  is  intermediate  be- 
tween the  posterior  and  the  anterior  root  neurones.  The 
decussating  axones  of  this  group  in  part  belong  to  the  pain  and 
temperature  path. 

Nucleus  Dorsalis  (Stillingi  and  Clarki). — This  column,  which 
was  discovered  by  Stilling,  is  composed  of  cell-bodies  measuring 


Posterior 
Jioot 


JSoot 


Fig.  147 — Mode  of  origin  of  anterior  and  posterior  roots  of  spinal  nerves. 
Diagrammatic.     {Bruhaker  and  Edinger  after  His.) 


from  40 II  to  109  y.  in  diameter  (Figs.  142  and  146).  It  forms  a 
most  striking  feature  of  the  gray  crescent  throughout  the 
thoracic  region.  It  constitutes  the  visceral  afferent  nucleus 
of  the  cord,  which  receives  the  non-sensory,  exci to-reflex  im- 
pulses from  viscera,  etc.  It  is  situated  near  the  medial  surface 
of  the  base  of  the  posterior  columna,  bounded  laterally  by  a 
curved  strand  of  posterior  root-fibers;  and  forms  a  continuous 
column  from  the  seventh  cervical  segment  to  the  second  lumbar 
segment.  The  column  is  largest  in  the  lower  two  thoracic  seg- 
ments, where  it  bulges  out  the  medial  surface  of  the  posterior 


ROOTS   OF   SPINAL  NERVES 


399 


columna.  It  is  represented  by  separated  groups  of  cell-bodies 
in  the  third  and  fourth  sacral  and  first  three  or  four  cervical 
segments  of  the  cord  and  in  the  afferent  part  of  the  nucleus  alge 
cinereae  in  the  medulla  oblongata.  The  limitation  of  the  dorsal 
nucleus,  as  an  unbroken  column,  to  the  region  of  the  white  rami 
communicantes  has  suggested  its  connection  with  the  sympathetic 
system;  and  it  is  the  terminal  nucleus  of  afferent  sympathetic 
fibers,  but  it  gives  rise  to  no  efferent  fibers  of  that  system. 
From  a  few  flat,  peripheral  cells  in  the  dorsal  nucleus  the  axones 


Fig.  148. — Typical  nerve  roots;   and  endogenous  neurones,   associative  and 

commissural. 
I.  Represents  those  neurones  that  form  the  radicular  tracts  of  the  posterior  column. 
2.  Neurones  connected  with  the  viscera  and  terminating  in  the  dorsal  nucleus.  3.  Simple 
spinal  reflex  neurones  terminating  in  the  anterior  column.  4.  Neurones  ending  in  the  nucleus 
of  the  posterior  column.  5.  Neurones  belonging  to  the  simplest  spinal,  sympathetic 
reflex  arcs.  6.  Small  neurones  that  form  the  marginal  fasciculus  of  Lissauer  and  end  in  the 
gelatinous  substance. 


run  forward  into  the  white  commissure.  Excepting  these  few 
fibers,  all  axones  from- the  dorsal  nucleus  proceed  into  the 
lateral  column;  there,  they  form  the  dorsal  spino-cerebellar 
tract  and,  for  a  short  distance,  some  of  them  ascend  within  the 
ventral  spino-cerebellar  tract.  The  several  dendrites  of  each 
neurone  ramify  richly  in  the  vicinity  of  the  cell-body.  Together 
with  the  cell-bodies,  the  dendrites  are  in  contact  relation  with 
fibers  of  the  posterior  roots  of  the  spinal  nerves.  The  nucleus 
dorsalis  receives  impulses  which  are  not  destined  to  produce 
sensations;  under  normal  conditions,  they  do  not  reach  con. 


400  THE    SPINAL   CORD 

sciousness  at  all;  they  excite  in  the  cerebellum  those  coordinat- 
ing impulses  that  control  the  sympathetic  functions  of  the 
organisms,  such  as  tonicity,  peristalsis,  secretion,  etc. 

Concerning  the  relation  of  the  gray  crescent  to  the  spinal 
nerves  (Fig.  146),  it  maybe  remarked,  here,  that  in  the  anterior 
columna  and  center  of  the  crescent  are  located  the  genetic  nuclei 
of  the  motor  or  efferent  fibers  (anterior  roots)  of  the  spinal 
nerves;  and  that  the  terminal  nuclei  of  the  sensory  fibers 
(posterior  roots)  of  the  spinal  nerves  are  located  chiefly  in  the 
posterior  columna,  but  also  in  the  center  and  anterior  columna  of 
the  crescent  in  the  cord,  and  in  the  nucleus  funiculi  gracilis  and 
nucleus  funiculi  cuneati  in  the  medulla  oblongata.  It  may  be 
stated,  further,  that  the  voluntary  motor  fibers  rise  in  the 
anterior  columna,  the  sympathetic  efferent  fibers  in  the  inter- 
medio-lateral  column;  while  the  sympathetic  afferent  fibers  end 
in  the  dorsal  nucleus  of  Clark,  and  the  common  sensory  fibers 
in  the  remainder  of  the  gray  crescent  and  in  the  nucleus  gracilis 
and  nucleus  cuneatus  of  the  medulla. 

The  gray  commissure  of  the  spinal  cord  (the  gray  anterior 
and  the  posterior  commissure)  is  the  vertical,  transverse  sheet  of 
gray  substance  connecting  the  two  crescents  together  (Fig.  139). 
This  commissure  (commissura  grisea)  completes  the  gray  matter 
of  the  cord.  It  unites  the  gray  crescents  together  a  little  in  front 
of  their  center,  except  in  the  lumbar  region  where  it  joins  their 
centers.  It  forms  the  floor  of  the  posterior  median  fissure  and 
in  front  is  in  relation  with  the  white  anterior  commissure.  It 
is  pierced  longitudinally  by  the  central  canal  of  the  spinal  cord 
which  is  surrounded  by  a  thick  envelope  of  substantia  gelatinosa. 
This  canal,  which  in  the  conus  medullaris  expands  into  the 
terminal  ventricle,  divides  the  commissure  into  two  parts.  That 
part  of  the  commissure  in  front  of  the  canal  is  the  gray  anterior 
commissure  {commissura  anterior  grisea)  and  that  behind  it  is 
the  posterior  commissure  {commissura  posterior,  Fig.  139).  The 
gray  commissure,  comprising  both  these  divisions,  is  composed 
of  spongy  and  gelatinous  substance  in  which  there  are  imbedded 
the  bodies  of  many  nerve  cells  and  a  large  number  of  medullated 
fibers.     The  medullated  fibers  are  derived  from  intrinsic  neu- 


ABOLITION  OF  PAIN  4OI 

rones  of  the  cord,  whose  centers  are  situated  in  the  commissure 
and  in  the  posterior  columna  and  center  of  the  crescent.  The 
crossing  fibers  of  the  gray  commissure  run  in  relation  to  the 
substantia  gelatinosa,  along  its  ventral  and  dorsal  surfaces;  the 
fibers  coursing  in  front  of  the  gelatinous  substance  radiate  into 
the  anterior  columna  and  center  of  the  crescent;  those  running 
behind  it  bend  backward  in  the  posterior  columna  toward  the 
entering  posterior  root-fibers.  The  posterior  commissure  is  said 
to  contain  a  long  sensory  tract  between  the  ventricle  and 
dorsal  surface  (Ciaglinski).  This  long  sensory  tract  is  found  in 
the  thoracic  portion  of  the  cord  and  the  discoverer  believes  it  to 
be  made  up  of  ascending  root-fibers  which  conduct  pain  and  tem- 
perature impulses.  It  is  in  need  of  further  investigation 
(Barker). 

Lesions  of  the  gray  substance,  as  in  syringomyelia,  may  com- 
pletely abolish  the  pain  and  temperature  senses  at  the  level  of  the 
lesion,  while  the  muscular  and  tactile  senses  are  preserved. 
Tactile  localization,  that  is,  the  recognition  of  the  location  of  a 
point  touched,  may  also  be  lost  as  the  result  of  a  lesion  in  the 
gray  substance.  A  lesion  in  one  crescent  may  abolish  the 
senses  of  pain,  temperature  and  tactile  localization  at  the  level 
of  the  lesion  on  the  same  side,  and  greatly  diminish  them  at  the 
same  level  on  the  opposite  side;  because  the  impulses  underlying 
these  sensations  decussate  to  a  considerable  extent  through  the 
gray  substance,  the  crossing  of  these  impulses  is  completed 
through  the  fibers  of  Gower's  tract.  Light  touch  and  pressure 
touch  are  also  reduced  by  lesions  of  the  gray  substance;  but,  as 
there  are  two  paths  for  such  impulses — one  through  the  gray 
matter  and  the  other  through  the  posterior  white  column 
on  the  same  side — they  are  never  abolished  by  such  lesions. 
Lesions  in  the  gray  matter  of  the  cord,  and  there  only,  do  not 
affect  the  conduction  of  impulses  that  underlie  the  sense  of 
position  and  movement,  tactile  discrimination  of  two  or  more 
points  of  simultaneous  contact,  recognition  of  vibration,  of 
size,  shape  and  form  in  three  dimensions,  of  weight,  of  rough- 
ness, and  of  texture.  If  the  lesions  affect  the  anterior  column 
of  the  gray  crescent,  flaccid  paralysis,  loss  of  reflexes  and 
26 


402  THE    SPINAL    CORD 

muscular  atrophy  result,  as  already  pointed  out  (Head  and 
Thompson:  Brain,  Vol.  29;  Head  and  Holmes:  Brain,  Vol.  34; 
P.  W.  Saunders:  Brain,  Vol.  36,  etc.). 

WHITE  MATTER  OF  THE  CORD 

The  white  matter  (Fig.  140)  of  the  spinal  cord  (substantia  alba 
spinalis)  is  disposed  in  its  peripheral  area  and  in  the  white  ante- 
rior commissure.  It  is  composed  of  meduUated  nerve  fibers 
(axones  and  collaterals)  imbedded  in  a  small  amount  of  neu- 
roglia, and  supported  by  a  connective  tissue  network  derived 
from  the  pia  mater.  Like  the  gray  matter  it  is  richly  supplied 
with  blood-vessels.  The  fibers  of  the  spinal  cord  run  trans- 
versely, dorso-ventrally  and  longitudinally. 

The  transverse  fibers,  which  are  usually  somewhat  oblique 
in  direction,  comprise  (i)  those  running  from  the  longitudinal 
tracts  into  the  gray  matter  or  out  of  the  gray  matter  into  such 
tracts;  (2)  the  axones  of  intrinsic  neurones  which  run  through 
the  gray  commissure  and  connect  the  two  crescents  at  nearly 
the  same  level;  and  (3)  the  fibers  of  the  white  commissure. 

The  transverse  fibers  of  the  gray  commissure  are  derived  from 
cell-bodies  located  in  the  posterior  columna  in  relation  with  in- 
coming root-fibers,  and  in  the  center  of  the  crescent.  As  they 
pass  over  to  the  opposite  crescent,  they  are  massed  along  the 
dorsal  and  ventral  surfaces  of  the  central  gelatinous  substance, 
in  the  posterior  and  anterior  gray  commissures.  The  fibers  of 
the  gray  commissures  radiate  in  the  anterior  columna  and  center 
of  the  crescent  and  form  contacts  with  intrinsic  neurones  of 
those  parts. 

The  white  anterior  commissure  of  the  spinal  cord  (commissura 
anterior  alba)  is  the  most  definite  lamina  of  transverse  fibers  in 
the  cord  (Fig.  139).  It  connects  the  anterior  and  lateral  white 
columns  of  the  cord  with  the  opposite  gray  crescent  and  the  two 
crescents  with  each  other.  It  is  located  in  front  of  the  gray 
anterior  commissure,  forming  the  floor  of  the  anterior  median 
fissure.  It  is  composed  of  medullated  fibers  belonging  to  (a) 
the  anterior  pyramidal  tract;  (b)  the  anterior  fasciculus  pro- 


FUNICULI   OF   CORD  403 

prius;  (c)  the  ventral  spino-cerebellar  and  spino- thalamic  tracts; 
(d)  it  comprises  the  crossed  fibers  to  the  anterior  roots  of  the 
spinal  nerves,  and  (e)  the  decussating  dendrites  between  the 
anterior  columnae. 

The  dorso-ventral  fibers  of  the  spinal  cord  (Fig.  145)  are  (a) 
those  of  the  anterior  roots  of  the  spinal  nerves,  in  their  course 
from  the  gray  matter  to  the  surface  of  the  cord;  (b)  those  of  the 
posterior  roots,  running  from  the  posterior-lateral  sulcus  to  their 
destination  in  the  gray  matter,  and  (c)  axones  of  intrinsic  neu- 
rones connecting  posterior  with  anterior  parts  of  the  crescent. 

The  longitudinal  fibers  comprise  most  of  the  white  matter  in 
the  cord,  forming  the  funiculus  anterior,  funiculus  lateralis  and 
funiculus  posterior  (Figs.  139  and  140).  These  three  great 
columns  occupy  the  anterior,  lateral  and  posterior  areas  of  the 
cord.  They  are  disposed  around  the  gray  crescent  in  bundles  or 
tracts.  The  tracts  which  make  up  the  funiculi  are  not  visible 
to  the  naked  eye,  nor  under  the  microscope  in  a  healthy  adult 
cord ;  they  have  been  located  by  embryological,  experimental  and 
pathological  investigations.  The  longitudinal  fibers  rise  in  the 
brain,  in  the  spinal  cord  and  in  the  spinal  ganglia;  some  run 
upward  and  others  downward,  constituting  the  tracts  of  the 
cord.  Thus  the  tracts  are  characterized  as  ascending,  descend- 
ing and  mixed  tracts.  The  mixed  tracts  are  the  fasciculi 
proprii.  They  are  made  up  of  T-branched  axones  and 
present  about  an  equal  intermingling  of  ascending  and  descend- 
ing fibers.  The  simple  fasciculi  or  tracts  are  so  named  as  to 
indicate  the  direction  of  their  growth  and  conduction:  the  first 
element  of  the  compound  noun  indicates  the  origin,  the  second 
element  designates  the  termination  of  the  tract.  The  tracts  of 
the  cord  are  as  follows: 
Funiculus  Anterior. — 

Fasciculus  proprius  anterior,  with  fasc.  longitudinalis 
medialis. 

Tr  actus  pyramidalis  anterior  or  fasc.  cerebrospinalis 
anterior. 

Fasciculus  tecto-spinalis  anterior. 

Fasciculus  reticulo-spinalis  anterior. 


Gowers'  tract. 


404  THE   SPINAL   CORD 

Ftiniculus  Lateralis. — 

Fasciculus  proprius  lateralis  with  CajaFs  bundle  of  the  dorsal 
horn. 

Tractus  pyramidalis  lateralis  or  fasc.  cerebrospinalis 
lateralis. 

Fasciculus  vestibulo-spinalis. 

Fasciculus  rubro-spinalis  (Monakow). 

Fasciculus  thalamo-spinalis. 

Fasciculus  reticulo-spinalis  lateralis. 

Fasciculus  tecto-spinalis  lateralis. 

Fasciculus  spino-cerebellaris  dorsalis  (Flechsig). 

Fasciculus  spino-vestibularis  (Horsley  and  Thiele). 

Fasciculus  spino-cerebellaris  ventralis. 

Fasciculus  spino-thalamicus. 

Fasciculus  spino-reticularis. 

Fasciculus  spino-tectalis. 

Fasciculus  spino-olivaris  (Helwig). 

Fasciculus  marginalis  (Lissauer). 
Funiculus  Posterior. — 

Fasciculus  proprius  posterior,  the  cornu-commissural  tract 
(Marie). 

Fasciculus  cuneatus  (Column  of  Burdach). 

Fasciculus  gracilis  (Column  of  GoU). 

Fasciculus  postero-medialis  descendens  (comma  tract 
(Schultze),  peripheral  bundle  (Hoche),  oval  tract  (Flechsig), 
sep to-marginal  tract  (Bruce  and  Muir),  median  triangular 
tract  (Gombault  and  Phillipe). 

Fasciculus  postero-lateralis  descendens  (Thiele  and  Horsley). 

The  methods  of  locating  tracts  of  fibers  may  be  summarized 
briefly,  as  follows: 

The  embryological  method  was  first  employed  successfully  by 
Flechsig.  He  found  that  nerve  fibers  when  first  laid  down  are 
naked  fibers  without  any  insulating  white  substance  of 
Schwann  enshea thing  them.  That  the  medullary  sheaths  are 
developed  at  different  times  and  that  the  meduUation  is  nearly 
coincident  with  the  beginning  of  function.  Thus  the  fibers  of 
motor  and  sensory  nerves  are  first  to  become  medullated,  since 


METHODS   OF   LOCATING  TRACTS  405 

life  cannot  be  sustained  without  the  automatic  mechanism. 
Second,  the  fasciculi  proprii  of  the  cord  are  medullated  and,  third, 
the  cerebellar  tracts.  At  this  stage  the  simple  automatic  and 
coordinating  mechanisms  are  complete.  Fourth,  the  voluntary 
motor  mechanism  is  established  by  the  medullation  of  the 
tracts  connecting  the  lower  neurones  with  the  cerebral  cortex, 
the  fibers  of  the  pyramidal  tracts  being  the  last  in  the  cord  to 
receive  their  medullary  sheaths.  This  last  begins  just  before 
birth.  Fibers  of  the  cerebrum  concerned  with  the  higher  psychic 
functions  of  the  brain  become  medullated  gradually,  year  after 
year,  keeping  pace  with  the  mental  development;  and  the  process 
of  medullation  there  is  not  completed  until  late  in  life  (Kaes). 
The  pathological  and  experimental  methods  depend  upon 
the  fact  that  a  nerve  fiber  when  severed  from  the  cell-body 
undergoes  degeneration  in  accordance  with  the  law  of  Waller. 
If  the  severed  fiber  be  above  the  cell-body,  the  degeneration 
occurs  above  the  lesion  and  is  called  ascending  degeneration; 
but,  if  the  degeneration  extends  from  the  lesion  down  the  nerve 
fiber,  the  cell-body  being  above,  then  the  condition  is  called 
descending  degeneration,  though  all  parts  of  the  severed  fibers 
really  degenerate  simultaneously.  Thus  by  studying  the  paths 
of  degeneration,  above  and  below  a  destructive  lesion  in  the 
human  cerebrospinal  axis,  the  various  tracts  of  fibers  have  been 
discovered  and  many  of  them  charted  and  traced  from  origin  to 
termination.  These  investigations  have  been  greatly  aided  by 
the  study  of  degenerations  in  the  brain  and  cord  of  lower  animals. 
These  degenerations  are  the  results  of  definite  experimental 
lesions,  as  cutting  of  certain  posterior  nerve  roots,  partial  sec- 
tion, hemisection  or  complete  section  of  the  spinal  cord,  etc. 
The  pathological  and  experimental  methods  are  commonly  called 
the  physiological  method. 

TRACTS  OF  THE  SPINAL  CORD 

The  antero-lateral  fasciciilus  proprius  [fasciculus  antero- 
lateralis  proprius)  occupies  the  deep  part  of  the  anterior  and 
lateral  columns  (Figs.  142  and  143).     It  embraces  the  anterior 


4o6  THE    SPINAL    CORD 

columna  of  gray  matter  and  covers  the  outer  surface  of  the 
center  of  the  crescent  and  the  base  of  the  posterior  columna. 
By  the  most  lateral  anterior  root-fibers  it  is  subdivided  into 
anterior  and  lateral  fasciculi.     It  approaches,  but  does  not  quite 
reach,  the  surface  of  the  cord.     Notice  that  it  is  separated  from 
the  anterior  median  fissure  by  the  anterior  pyramidal  tract,  and 
that  the  lateral  pyramidal,   the  spino-cerebellar   and   spino- 
thalamic tracts,  etc.,  run  between  it  and  the  surface  of  the  cord. 
Behind,  it  is  in  relation  with  the  lateral  pyramidal  tract.     The 
antero-lateral   fasciculus  proprius  is   composed  of  ascending 
and  descending  fibers  which  are  the  T-branches  of  axones  from 
the  gray  crescent.     It  is  largely  a  short  fiber  tract,  associative 
and    commissural    in  function.     That    part    situated    in    the 
anterior  column,   the  anterior  fasciculus  proprius,  is  largely 
commissural,  between  the  anterior  columnae;  while  the  lateral 
fasciculus  proprius  is  chiefly  associative,  and  connects  different 
segments  of  the  cord  on  the  same  side.     That  part  of  the 
lateral    fasciculus    proprius    which    intervenes    between    the 
posterior  columna  and  the  lateral  pyramidal  tract,  and  inter- 
mingles somewhat  with  the  marginal  fasciculus,  is  called  by 
Cajal  the  bundle  of  the  dorsal  horn.     It  rises  from  the  cell-bodies 
in  the  substantia  gelatinosa  and  caput  of  the  posterior  columna; 
its  fibers  are  small  and  short.     As  a  rule,  all  fibers  of  the 
fasciculus  proprius  which  are  next  the  gray  substance  are 
short,  the  longer  ones  run  farther  and  farther  from  the  gray 
crescent.     The  antero-lateral  fasciculus  proprius  is  continued 
in  the  substantia  reticularis  of  the  medulla,  and  the  reticular 
formation  of  pons  and  mid-brain,  constituting  a  short  fiber 
tract  which  extends  from  the  lower  part  of  the  cord  to  the  basal 
gangHa  of  the  cerebrum.     A  part  of  the  anterior  fasciculus 
proprius   is   continued   into    the   medial   longitudinal  bundle 
(fasciculus  longitudinalis  medialis). 

The  medial  {posterior)  longitudinal  bundle  is  composed  of  an 
ascending  and  a  descending  strand  of  fibers  (Figs.  142  and  143). 
The  ascending  strand  rises  from  the  anterior  columna  in  each 
segment  of  the  spinal  cord  and  runs  upward  to  the  motor  nuclei 
of  cerebral  nerves  and  terminates  in  them.     Perhaps  a  few  fibers 


MOTOR   AND    REFLEX  BUNDLES  407 

reach  the  thalamus.  It  ascends  just  ventro-medial  to  the 
anterior  columna  in  the  cord;  in  the  medulla,  it  runs  between 
the  head  of  the  anterior  columna  and  the  pyramidal  decussa- 
tion, then  just  lateral  to  the  fillet  decussation,  after  which,  it 
takes  its  doros-medial  position  along  the  raphe.  Its  function 
is  rejkx.  The  descending  strand  is  the  anterior  reticulospinal 
tract.  It  rises  from  all  the  nuclei  of  the  reticular  formation 
but  chiefly  from  the  nuclei  centrales  and  the  nucleus  lateralis 
medius  in  the  pons.  Forming  a  part  of  the  medial  longitudinal 
bundle  of  the  same  side,  its  fibers  end  in  the  crescent  as  it 
descends  the  cord.  Within  the  lateral  funiculus,  descends  the 
lateral  reticulospinal  tract.  This  tract  has  the  same  origin  and 
termination  as  the  anterior  reticulo-spinal  tract  except  that  it 
decussates.  It  crosses  near  its  origin  right  through  the  medial 
longitudinal  bundles.  Both  reticulo-spinal  tracts  extend  to 
the  lower  part  of  the  cord. 

The  anterior  pyramidal  tract  {fasciculus  cerebrospinalis 
anterior),  occupies  a  thin  area  next  the  anterior  median  fissure 
(Figs.  142  and  143).  It  is  the  direct  continuation  of  about  10 
per  cent,  of  the  pymmidal  tract  in  the  medulla.  It  is  said  to 
be  absent  in  15  per  cent,  of  human  cords;  in  these  cases  there 
is  complete  decussation  to  the  lateral  funiculus,  as  in  the  cat. 
In  the  mole  the  whole  pyramidal  tract  descends  the  anterior 
funiculus  without  division  or  decussation.  The  fibers  of 
the  anterior  pyramidal  tract  rise  from  the  giant  cells  of  Betz, 
whose  bodies  are  situated  in  the  anterior  central  gyrus  of  the 
cerebrum.  As  the  tract  descends  in  the  cord,  the  fibers  decus- 
sate through  the  white  anterior  commissure,  and  terminate  in 
relation  with  the  cells  of  the  opposite  gray  crescent,  probably, 
in  the  posterior  columna.  It  reaches  to  the  fifth  sacral  seg- 
ment (Collier).  Imbedded  in  the  anterior  pyramidal  tract 
is  a  small  strand  first  described  by  Held,  the  anterior  tecto- 
spinal fasciculus. 

Anterior  Tectospinal  Bundle  (Figs.  142  and  143). — Held 
called  it  the  fasciculus  longitudinalis  ventralis.  It  occupies  a 
very  narrow  strip  in  the  anterior  column  just  beside  the  en- 
trance of  the  anterior  median  fissure.     The  anterior  tecto- 


408  THE    SPINAL    CORD 

spinal  bundle  has  already  been  traced  from  its  origin  in  the 
superior  quadrigeminal  colliculus,  through  the  dorsal  tegmented 
decussation  (Meynerti)  to  a  position  in  the  mid-brain  ventro- 
lateral from  the  medial  longitudinal  bundle.  It  descends  in 
that  relative  position  through  the  pons  and  half  the  medulla; 
near  the  pyramidal  decussation  the  anterior  and  medial 
longitudinal  bundles  are  brought  together  and  lie  between 
that  decussation  and  the  isolated  head  of  the  anterior  columna; 
they  diverge  upon  entering  the  cord  and  remain  separate  to 
the  end.  The  anterior  tecto-spinal  fasciculus  ends  in  both 
anterior  columnae  (Collier).  It  forms  the  middle  link  in  the 
ocular  and  pupillary  reflex  arcs. 

The  vestibulo -spinal  tract  {fasciculus  vestihulospinalis) 
rises  in  the  lateral  vestibular  nucleus  (of  Deiters)  and  terminates 
in  the  gray  matter  of  the  cord.  The  vestibulo-spinal  tract,  in 
section,  forms  a  crescentic  zone  of  the  cord  reaching  from  the 
anterior  pyramidal  tract  outward  and  backward,  over  the 
antero-lateral  fasciculus  proprius,  to  the  middle  of  the  lateral 
column.  It  is  divided  by  the  anterior  roots  of  the  spinal 
nerves  into  an  anterior  and  a  lateral  fasciculus.  The  lateral 
vestibulo -spinal  tract  is  intermediate  in  position  between  the 
fasciculus  proprius  and  Cowers*  tract,  the  latter  separates  it 
from  the  surface  of  the  cord.  It  is  more  or  less  intermingled 
with  the  rubro-spinal,  thalamo-spinal;  lateral  tecto-spinal  and 
lateral  reticulo-spinal  tracts,  though  the  former  two  run  largely 
dorsal  to  it.  The  anterior  vestibulospinal  tract  is  blended 
superficially  with  the  anterior  fibers  of  the  spino-thalamic  tract 
and  deeply  with  fibers  to  and  from  the  reticular  formation. 
The  vestibulo-spinal  tract  joins  the  vestibular  nerve  directly 
with  the  motor  spinal  nerves.  It  also  forms  a  descending 
link  in  the  cerebellar  arc  of  equilibrium;  the  other  descending 
links  of  the  arc  are  the  cortico-nuclear  fibers  of  Purkinje's 
cells,  going  to  the  nucleus  fastigii;  and  the  fastigio-bulbar  fibers 
which  end  in  the  nucleus  of  Deiters.  The  vestibulo-spinal 
tract  presides  over  muscle  tone,  coordination  and  equilibrium. 

In  the  ventral  portion  of  the  lateral  vestibulo-spinal  tract, 
the   lateral  reticulo-spinal  tract   descends   from    the   opposite 


TRACT   OF   COWERS  409 

nuclei  of  the  reticular  formation  in  the  brain-stem;  and,  be- 
hind that,  descends  the  lateral  tectospinal  tract,  which  rises 
in  the  tectum  on  the  same  side,  chiefly  in  the  superior  colliculus. 
Both  tracts  terminate  in  the  gray  matter  of  the  cord,  probably 
in  the  anterior  columna.  Dorsal  to  the  vestibulo-spinal  tract, 
and  blended  with  it  to  some  extent,  run  the  rubrospinal  and 
thalamospinal  tracts  to  be  described  below:  they  separate  the 
vestibulo-spinal  tract  from  the  lateral  pyramidal  tract. 

Gowers'  Tract. — This  is  a  compound  funiculus  composed  of 
several  fasciculi.  It  forms  the  antero-lateral  surface  of  the 
cord  from  a  line  midway  between  the  posterior  and  anterior 
roots  of  the  spinal  nerves  forward  almost  to  the  anterior  pyrami- 
dal tract.  Behind,  it  is  in  contact  with  the  dorsal  spino- 
cerebellar tract.  It  intermingles  with  the  spino-olivary  tract 
just  lateral  to  the  anterior 'nerve-roots,  and  with  the  vestibulo- 
spinal tract  medial  to  those  roots.  Gowers'  tract,  though  it 
possesses  many  terminations,  has  one  common  origin  from  the 
basal  region  of  the  anterior  columna  in  both  crescents.  Some 
writers  claim  that  Gowers^  tract  rises  from  the  base  of  the 
posterior  columna,  especially  from  the  dorsal  nucleus  of  Clark; 
and  there  is  evidence  that  a  number  of  fibers  from  the  dorsal 
nucleus  do  ascend  within  it  for  a  short  distance,  but  they  soon 
trend  backward  into  the  dorsal  spino-cerebellar  fasciculus.  The 
larger  number  of  fibers  in  Gowers'  tract  rise  in  the  opposite 
anterior  columna  and  cross  over  through  the  white  commissure; 
the  uncrossed  fibers  rise  in  relation  with  axones  that  cross 
through  the  gray  commissure  from  cell-bodies  in  the  opposite 
crescent,  so  the  conduction  path  to  which  the  tract  belongs  is 
wholly  a  crossed  one.  The  tract  of  Gowers  runs  as  one  com- 
pact funiculus  through  the  spinal  cord.  In  the  brain-stem,  it 
separates  into  several  fasciculi  which  terminate  in  the  reticular 
nuclei,  the  cerebellar  cortex,  the  tectum,  the  substantia  nigra, 
the  thalamus,  etc.  Four  of  these  fasciculi  are  commonly 
distinguished  by  specific  names;  the  spino-reticular,  spino- 
tectal, ventral  spino-cerebellar,  and  spino-thalamic.  The  two 
latter  are  the  more  important.  The  spino-reticular  fasciculus 
ends  in  the  nuclei  of  the  reticular  formation,  chiefly  in  the  in- 


4IO  THE    SPINAL   CORD 

ferior  lateral  nucleus  of  the  medulla;  and  the  reticulo-cerebellar 
tract  continues  its  conduction  to  cerebellar  cortex.  The  spino- 
tectal  fasciculus  terminates  in  the  superior  and  inferior  quad- 
rigeminal  coUiculi  of  the  tectum.  It  forms  a  link  in  a  reflex 
arc. 

The  ventral  spino-cerebellar  fasciculus  ascends  the  cord  and 
brain-stem  lateral  to  the  spino-thalamic  tract.  It  forms  the 
surface  of  the  cord  from  the  mid-lateral  line  nearly  to  the  an- 
terior roots  of  the  spinal  nerves.  Running  up  the  surface  of 
the  lateral  column  of  the  cord  and  medulla,  it  continues  through 
the  lateral  part  of  the  reticular  formation  of  the  pons,  in  the 
same  lateral  relation  to  the  spino-thalamic  tract,  until  it  passes 
the  root  of  the  trigeminal  nerve;  there,  it  separates  from  the 
spino-thalamic  tract,  winds  backward  over  the  dorso-lateral 
surface  of  brachium  conjunctivum,  enters  the  superior  medul- 
lary velum  of  the  cerebellum,  decussates  with  its  fellow  of  the 
opposite  side  and  terminates  in  the  cortex  of  the  vermis  superior 
cerebelli.  The  ventral  spino-cerebellar  fasciculus  probably 
carries  pain,  temperature  and  localizing  tactile  impulses  which, 
under  normal  conditions,  are  non-sensory;  they  excite  coordi- 
nating reflex  impulses.  But,  if  the  impulses  are  very  powerful, 
they  excite  the  appropriate  reflexes  and  then  overcoming  the 
synaptic  resistance  flow  on  to  the  conscious  centers  in  the  cere- 
brum by  way  of  the  brachium  conjunctivum  and  rubro- thalamic 
tract.  The  ventral  spino-cerebellar  fasciculus,  alone,  is  called 
Gowers'  tract  by  some  anatomists. 

The  spino-thalamic  fasciculus  is  the  superficial  anterior  and 
the  deep  lateral  part  of  Gowers'  tract.  It  forms  a  long,  thin 
crescent  in  sections  of  the  cord.  By  the  anterior  roots  of  the 
spinal  nerves  it  is  divided  into  an  anterior  and  a  lateral  fascicu- 
lus, like  the  vestibulo-spinal  tract,  which  descends  beneath 
it.  The  lateral  spino-thalamic  fasciculus  is  covered  throughout 
the  spinal  cord  by  the  ventral  spino-cerebellar  tract;  but  the 
anterior  fasciculus  follows  the  surface  of  the  cord  in  front  of 
the  anterior  roots,  where  it  is  intermingled  with  the  anterior 
vestibulo-spinal  tract.  In  the  brain-stem,  the  spino-thalamic 
tract  ascends  medial  to  the  ventral  spino-cerebeflar  tract  to  the 


PAIN   AND   TEMPERATURE   PATHS  41I 

point  of  divergence  in  the  pons  at  the  level  of  the  root  of  the 
trigeminal  nerve;  above  the  level  of  the  trigeminal  root  the 
spino- thalamic  tract  continues  into  the  tegmentum  of  the 
mid-brain,  accompanied  by  the  spino-tectal  fasciculus;  the  latter 
ends  in  the  quadrigeminal  colliculi  of  the  tectum,  the  former  con- 
tinues through  the  tegmentum  and  terminates  in  the  ventral 
part  of  the  lateral  nucleus  of  the  thalamus.  The  spino-thalamic 
tract  carries  impulses  of  pain,  heat,  cold,  light  touch,  pressure 
touch,  and  tactile  localization.  Of  these  impulses  the  anterior 
spino-thalamic  fasciculus  carries  only  light  touch  and  pressure 
touch,  according  to  W.  Page  May;  the  lateral  fasciculus  con- 
veys the  remainder.  Though  all  these  impulses  just  enumer- 
ated traverse  the  spino-thalamic  tract,  each  one  travels  through 
its  own  specific  bundle  and,  as  a  result  of  localized  lesion,  may  be 
lost  without  any  of  the  others  being  affected,  excepting  only 
impulses  of  light  touch  and  pressure.  They  are  not  lost  be- 
cause there  is  a  second  path  for  them,  an  uncrossed  one,  in  the 
posterior  column.  This  specificity  of  the  lateral  column  is 
in  accord  with  the  law  that  second  order  afferent  neurones  form 
specific  tracts. 

Spino-olivary  Fasciculus. — On  the  surface  of  the  cord  and 
just  lateral  to  the  anterior  roots  of  the  spinal  nerves,  there 
runs  a  small  tract,  triangular  in  section,  commonly  called  the 
triangular  tract  of  Helwig.  It  is  the  custom  at  present  to  de- 
scribe it  as  the  spino-olivary  fasciculus,  because  of  the  as- 
sumption that  it  rises  in  the  gray  matter  of  the  cord  and 
terminates  in  the  inferior  olive  of  the  medulla;  but  its  origin, 
termination  and  function  have  not  been  positively  determined. 

Dorsal  Spino-cerebellar  Fasciculus  (fasciculus  spino-cere- 
bellaris  dorsalis,  direct-cerebellar  tract  of  Flechsig). — Both 
spino-cerebellar  tracts  are  located  in  the  lateral  column  of  the 
spinal  cord;  hence,  they  are  best  distinguished  by  the  adjectives 
ventral  and  dorsal.  The  dorsal  spino-cerebellar  tract  forms  the 
dorsal  half  of  the  lateral  surface  of  the  cord,  as  the  ventral 
spino-cerebellar  tract,  assisted  by  the  spino-olivary  fasciculus, 
forms  the  ventral  half  of  that  surface.  It  covers  the  lateral 
pyramidal  tract  by  its  deep  surface.     Its  dorsal  border  rests 


412  THE    SPINAL   CORD 

against  the  marginal  tract  of  Lissauer,  which  separates  it  from 
the  posterior  roots  of  the  spinal  nerves.  Below  the  second 
lumbar  segment  its  absence  allows  the  lateral  pyramidal  tract 
to  come  to  the  surface.  The  dorsal  spino-cerebellar  tract  runs 
from  the  dorsal  nucleus  (Clarki)  of  the  cord  to  the  superior 
worm  of  the  cerebellum.  Its  fibers  are  axones  of  vesicular  cells 
in  that  nucleus.  In  the  medulla,  crossing  over  to  the  posterior 
column,  it  enters  the  restiform  body  and  proceeds  to  the  cortex 
of  the  superior  vermis  cerebelli  on  both  sides.  It  conveys  non- 
sensory,  sympathetic  impulses,  received,  especially,  from  the 
viscera.  In  the  dorso-lateral  part  of  the  spino-cerebellar  tract 
is  a  small  strand  of  fibers  discovered  by  Horsley  and  Thiele  in 
1 901 ,  called  the  spino-vestibular  tract.  It  rises  in  the  lumbo-sacral 
region  of  the  cord  and,  ascending  along  the  surface  of  the  dorsal 
spino-cerebellar  tract  to  the  medulla,  winds  inward  dorsal  to 
the  restiform  body  and  terminates  in  the  nucleus  of  the 
vestibular  nerve. 

The  lateral  pyramidal  tract  (fasiculus  cerebro spinalis  lateralis) 
forms  a  considerable  part  of  the  lateral  column  of  the  spinal 
cord  (Figs.  142  and  143).  It  is  covered,  superficially,  by 
the  dorsal  spino-cerebellar  tract  in  the  cervical  and  thoracic 
cord;  but  in  the  lumbar  and  sacral  cord  it  forms  part  of  the 
surface.  Its  deep  surface  is  in  relation  with  the  lateral  fascicu- 
lus proprius,  its  ventral  border  with  the  rubro-spinal  and  thal- 
amo-spinal  tracts,  and  its  dorsal  border  with  the  marginal  bun- 
dle. The  fibers  composing  it  are  axones  of  Betz's  cells  in  the 
anterior  central  gyrus  of  the  cerebral  cortex.  They  rise  with 
those  of  the  anterior  pyramidal  tract,  and  the  two  run  as  one 
tract  down  through  the  genu  and  anterior  two-thirds  of  the 
occipital  part  of  the  internal  capsule,  the  middle  three-fifths  of 
the  basis  pedunculi,  the  basilar  longitudinal  fibers  of  the  pons 
and  the  pyramid  of  the  medulla.  In  the  medulla  the  two  tracts 
separate.  The  lateral  tract,  comprising  four-fifths  of  the  pyra- 
mid, decussates  with  its  fellow  through  the  anterior  median 
fissure,  pierces  the  anterior  gray  columna  and  descends  with 
some  uncrossed  fibers  in  the  lateral  column  of  the  cord.  It 
terminates  in  relation  with  the  baso-lateral  cell-bodies  within 


COURSE    OF   PYRAMIDAL  TRACTS  413 

the  posterior  columna,  according  to  Schafer,  Collier  and  others. 
The  anterior  tract  follows  the  anterior  median  fissure  as  already- 
described.  Both  end  chiefly  in  the  gray  crescent  opposite  to 
their  cortical  origin.  According  to  Marchi,  lo  or  20  per 
cent,  of  the  fibers  remain  uncrossed.  The  pyramidal  tracts 
are  the  cerebral  motor  tracts.  By  them  motor  and  inhibitory 
impulses  are  carried  to  the  cord. 

Only  in  the  higher  primates  does  the  pyramidal  tract  divide 
in  the  medulla  into  two  fasciculi:  in  mammals  generally  and 
in  the  lower  monkeys  it  is  undivided.  There  is  one  known  mam- 
mal in  which  it  descends  the  anterior  funiculus  without  decus- 
sation, the  mole.  In  all  other  mammals  below  primates,  it 
decussates  en  masse  to  the  opposite  side;  it  descends  the  dorsal 
part  of  the  lateral  funiculus,  near  the  posterior  columna,  in 
carnivora  and  in  the  rabbit;  and  it  runs  down  the  ventral  part 
of  the  posterior  funiculus  in  certain  herbivora,  such  as  the  red 
squirrel,  chipmunk,  guinea-pig,  mouse,  white  rat,  etc.  (Ran- 
son:  Am.  Jour.  Anat.,  Vol.  14,  and  Jour.  Comp.  Neurol.,  Vol.  24. 
Simpson:  Jour.  Comp.  Neurol.,  Vol.  24). 

Lesions. — The  pyramidal  tracts  (especially  the  lateral)  are 
involved  in  lateral  sclerosis  and  in  amyotrophic  lateral  sclerosis; 
and,  as  a  consequence  of  it,  both  voluntary  and  inhibitory  im- 
pulses from  the  brain  are  interfered  with,  hence  the  spastic 
paralysis  and  exaggerated  reflexes.  The  pyramidal  tract  may 
be  more  or  less  involved  in  insular  sclerosis  and  in  bulbar  paraly- 
sis, and  the  symptoms  vary  with  the  amount  of  sclerosis.  De- 
generation of  the  gray  matter  and  of  the  pyramidal,  spino- 
cerebellar, marginal  and  posterior  tracts  has  been  demonstrated 
in  Friedreich's  hereditary  ataxia,  and  the  involvement  of  the 
pyramidal  tracts  explains  the  spastic  paralysis  which  affects 
both  arms  and  legs.  In  ataxic  paraplegia  (Gowersi)  there  is 
diffuse  sclerosis  of  the  lateral  and  posterior  columns  of  the  cord. 
It  is  the  degeneration  in  the  pyramidal  tracts  that  causes  the 
spastic  gait,  incoordinated  arm  movements  and  early  increase 
of  the  reflexes,  observed  in  that  affection. 

Rubro-spinal  and  Thalamo-spinal  Fasciculi. — These  two 
tracts  in  close  association  descend  the  cord  ventral  to  the  lateral 


414  THE    SPINAL    CORD 

pyramidal  tract  and  subjacent  to  the  spino-cerebellar  tracts. 
They  are  somewhat  intermingled  with  the  dorsal  fibers  of  the 
lateral  vestibulo-spinal  tract,  which,  for  the  most  part,  is  in 
front  of  them.  The  rubrospinal  fasciculus  has  been  more 
perfectly  traced  and  is  better  understood,  though  it  is  claimed 
that  a  greater  number  of  fibers  from  the  thalamus  descend 
through  this  region  than  from  the  red  nucleus.  The  fibers  from 
the  red  nucleus  constitute  the  rubro-spinal  tract  of  Monakow. 
It  extends  as  far  as  the  first  lumbar  segment  and  ends  in  the 
gray  crescent.  Its  origin  in  the  nucleus  ruber,  its  crossing 
through  the  ventral  tegmental  decussation  (Foreli)  and  its 
course  down  the  brain  stem  have  been  described.  The  rubro- 
spinal tract  is  descending  in  direction.  It  carries  coordinating 
impulses  to  the  lower  motor  neurones  presiding  over  locomotion 
(Horsley) .  The  thalamo-spinal  fasciculus  probably  originates 
in  the  lateral  nucleus  of  the  thalamus  and  possibly  in  the  hypo- 
thalamic nucleus.  We  have  no  positive  evidence  of  its  decus- 
sating like  the  rubro-spinal  tract  which,  lower  down,  it  accom- 
panies; it  appears  to  be  an  uncrossed  tract.  The  thalamo- 
spinal  tract,  like  the  rubro-spinal,  terminates  in  the  gray  matter 
of  the  cord  in  connection  with  the  anterior  root  neurones. 
Manifestly  its  function  is  of  a  reflex  nature. 

The  marginal  fasciculus  of  Lissauer  (fasciculus  marginalis) 
lies  upon  the  apex  of  the  posterior  columna,  lateral  to  the  main 
bundles  of  the  posterior  root-fibers;  it  touches  the  surface, 
superficially;  and  its  deep  border  fuses  with  the  stratum  zonale 
of  the  gelatinous  substance  of  Rolando.  The  marginal  tract  is 
composed  of  small  fibers,  most  of  them  non-medullated  (Ran- 
son),  from  the  lateral  fascicles  of  the  posterior  roots  of  the  spinal 
nerves;  they  are  axones  of  the  small  bipolar  cells  of  the  spinal 
ganglia.  Dividing  T-like  as  they  enter  the  cord,  their  ascending 
and  descending  rami  pursue  a  short  vertical  course  and,  then, 
terminate  in  the  gelatinous  substance  of  the  posterior  columna. 
Interspersed  through  the  marginal  tract,  there  are  many  medul- 
lated  fibers  of  the  lateral  fasciculus  proprius,  fibers  belonging 
to  the  ''bundle  of  the  dorsal  horn.''  The  function  of  the  mar- 
ginal tract  is  unknown.     It  has  been  suggested  by  Ranson  and 


STRUCTURE   OF   POSTERIOR   COLUMN  415 

Others,  but  without  supporting  data,  that  it  conveys  impulses 
of  pain  and  temperature.  Others  suggest  a  sympathetic  func- 
tion (Am.  Jour.  Anat.,  Vol.  16;  Anat.  Rec,  Vol.  8,  p.  119; 
Jour.  Comp.  Neurol.,  Vol.  24). 

Tracts  of  the  Posterior  Column  of  the  Cord  (Figs.  142, 143). — 
In  the  posterior  column  of  the  spinal  cord,  there  are,  firsts  two 
ascending  and  two  descending  tracts,  derived  from  posterior 
nerve  roots;  second,  the  posterior  fasciculus  proprius,  which  is 
in  the  ventral  part  of  the  columna;  and,  third,  the  entry  zone 
occupied  by  the  incoming  fibers  of  the  posterior  roots. 

Entry  Zone  (Figs.  142  and  143), — Over  the  apex  and  along 
the  medial  surface  of  the  posterior  columna  of  gray  substance 
the  posterior  roots  of  the  spinal  nerves  enter  the  cord  and  divide 
T-like  into  ascending  and  descending  branches.  The  name 
entry  zone  is  well  applied  to  this  region.  The  presence  of  hori- 
zontal fibers  distinguishes  the  entry  zone  from  the  longitudinal 
tracts.  The  root-fibers  of  small  caliber  and  many  collaterals 
very  soon  enter  the  gray  substance.  The  large  fibers,  in  part, 
enter  the  dorsal  nucleus,  but  the  greater  number  form  the  longi- 
tudinal tracts  of  the  posterior  column.  The  ascending  fibers 
begin  their  upward  course  in  the  entry  zone.  As  they  ascend, 
the  posterior  gray  column  is  crowded  lateralward  by  the 
entrance  of  new  root-fibers  in  the  succeeding  upper  segments. 
So  the  fibers  near  the  septum  are  those  which  enter  low  down 
in  the  cord  and  those  close  to  the  posterior  columna  are  of 
recent  entrance  into  the  cord.  The  descending  T-branches  ^nd 
collaterals  of  the  posterior  roots  begin  their  descent  also  in  the 
entry  zone.  Some  of  them  run  a  long  course,  even  from  the 
sixth  cervical  to  the  sacral  segments  (Collier).  The  greater 
number  are  much  shorter.  From  above  downward  they  trend 
in  a  dorso-medial  direction,  approaching  the  median  septum, 
and,  after  a  considerable  downward  course,  they  plunge  forward 
through  the  white  column  to  end  in  the  posterior  columna. 
These  ascending  and  descending  fibers,  whose  origin  is  in  the 
spinal  ganglia  on  the  posterior  roots  of  the  spinal  nerves,  to- 
gether with  the  fibers  of  the  posterior  fasciculus  proprius  which 
rise  in  the  posterior  columna,  constitute  the  longitudinal  tracts 


41 6  THE    SPINAL   CORD 

of  the  posterior  column  of  the  spinal  cord.  That  posterior 
column  is  undivided  by  any  sulcus  below  the  eighth  thoracic 
segment,  where  the  posterior  intermediate  furrow  and  septum 
fade  away;  but,  above  that  level,  it  is  subdivided  into  two  dis- 
tinct ascending  tracts,  a  postero-medial,  the  fasciculus  gracilis, 
and  a  posterolateral,  the  fasciculus  cuneatus  (Fig.  142). 
These  two  tracts  are  alike  in  constitution.  They  have  the  same 
function,  carrying  impulses  that  excite  the  following  sensations: 
of  posture  and  movement  (muscle-sense),  of  two  or  more  simul- 
taneous contacts  (tactile  discrimination),  of  size,  shape  and  form 
in  three  dimensions,  of  weight,  of  vibration,  of  roughness  and 
texture  (?),  of  light  touch  and  pressure  touch.  The  impulses 
produced  by  light  touch  and  pressure  also  ascend  another  path 
in  the  opposite  lateral  column.  The  two  ascending  tracts  of 
the  posterior  column  of  the  spinal  cord  differ  only  in  length; 
the  fibers  of  the  fasciculus  gracilis  come  from  the  spinal  nerves 
below  the  eighth  thoracic,  while  those  of  the  fasciculus  cuneatus 
come  entirely  from  thoracic  and  cervical  nerves. 

Fasciculus  Gracilis  (ascending  postero-medial  tract,  GolFs 
column) . — This  tract  may  be  said  to  begin  at  the  entrance  of 
the  posterior  root  of  the  coccygeal  nerve  (Figs.  142  and  143). 
It  ascends  along  the  posterior  median  septum  to  the  nucleus 
funiculi  gracilis  of  the  medulla.  Up  to  the  lower  thoracic  nerves 
it  gradually  enlarges,  due  to  the  acquisition  of  successive  pos- 
terior root-fibers;  and  in  this  region,  excepting  only  the  entry 
zone  and  the  descending  branches  of  the  posterior  roots,  it 
comprises  the  whole  extrinsic  part  of  the  posterior  column.  Its 
size  is  not  increased  in  the  upper  three-fourths  of  the  cord,  where 
the  posterior  intermediate  furrow  separates  it  from  the  fasciculus 
cuneatus;  it  rather  diminishes  above  the  fifth  thoracic  nerve, 
as  no  root-fibers  enter  it  above  that  level  and  collaterals  leave 
it  in  every  successive  segment  to  end  within  the  gray  crescent. 
In  depth  it  almost  reaches  the  gray  commissure,  near  which  it 
intermingles  with  the  posterior  fasciculus  proprius.  Its  fibers 
are  the  ascending  rami  of  T-branched  axones  originating  in  the 
spinal  ganglia. 


DESCENDING  EADICULAR  TRACTS  417 

Arriving  at  the  clava,  all  the  fibers  of  the  fasciculus  gracilis 
arborize  and  end  in  the  nucleus  funiculi  gracilis. 

Fascictilus  Cuneatus  (ascending  posterolateral  tract,  Bur- 
dach's  column). — Beginning  in  the  middle  thoracic  segments 
(Fig.  142)  the  fasciculus  cuneatus  ascends  between  the  entry 
zone  and  the  fasciculus  gracilis  to  the  nucleus  funiculi  cuneati 
of  the  medulla.  It  acquires  new  fibers  from  every  spinal  nerve 
above  its  origin  and  grows  stronger  up  to  the  first  cervical  nerve. 
In  section  it  is  wedge-shaped,  being  broadest  at  the  surface;  the 
edge  of  the  wedge  almost  touches  the  junction  of  the  posterior 
columna  and  posterior  commissure,  the  posterior  fasciculus 
proprius  intervenes.  Its  fibers  are  ascending,  and  are  branches 
of  the  axones  of  spinal  ganglia  cells,  like  the  fasciculus  gracilis. 
In  the  nucleus  funiculi  cuneati  all  its  fibers  arborize  and  termi- 
nate (Collier). 

Descending  Tracts  Derived  from  Posterior  Roots. — The 
descending  fibers  from  the  posterior  roots  of  the  spinal  nerves 
arrange  themselves  somewhat  roughly  into  two  tracts,  a  postero- 
lateral and  a  postero-medial  (Figs.  142  and  143).  These  de- 
scending radicular  tracts  greatly  expand  and  multiply  the  ter- 
minal relations  of  the  posterior  root-fibers. 

The  descending  postero-medial  tract  (Figs.  142  and  143) 
has  received  various  names  at  different  levels.  In  the  cervical 
and  upper  nine  thoracic  segments,  it  is  the  comma  tract  (of 
Schultze),  situated  in  the  fasciculus  cuneatus.  Its  ventral  part 
disappears  in  the  posterior  columna  above  the  tenth  segment, 
but  the  remainder  continues  down  the  cord.  Shifting  its  posi- 
tion in  a  dorso-medial  direction,  it  takes  its  place  along  the 
posterior  surface  in  the  lower  thoracic  segments,  forming  the 
peripheral  bundle  (of  Hoche),  and  then  takes  up  its  position 
beside  the  median  septum.  It  continues  in  that  situation  to 
the  end  of  the  cord,  and  is  called,  in  succession)  the  oval  tract 
(of  Flechsig),  in  the  lumbar  segments  and  the  septo-marginal 
tract  (of  Bruce  and  Muir),  or  the  median  triangular  tract  (of 
Gambault  and  Phillipe)  in  the  sacral  and  coccygeal  segments. 
Fibers  from  the  spinal  nerves  enter  this  postero-medial  descend- 
ing tract  in  the  cervical,  thoracic,  and,  at  least,  the  upper  lumbar 
27 


41 8  THE   SPINAL   CORD 

segments.  After  a  variable  course  within  the  tract,  the  fibers 
plunge  forward  into  the  posterior  columna  of  gray  substance 
where  they  terminate. 

The  descending  postero-lateral  tract  (Fig.  143),  situated  at 
the  posterior  surface  of  the  cord  medial  to  the  entry  zone,  in 
the  lumbo-sacral  region,  appears  to  have  been  first  described  by 
Thiele  and  Horsley.  It  is  derived  from  the  posterior  roots  of 
the  lower  spinal  nerves,  hence  it  descends  close  to  the  entry 
zone.  In  section  it  is  triangular.  Its  fibers  terminate  in  the 
posterior  columna  of  gray  substance. 

Posterior  Fasciculus  Proprius  {fasciculus  posterior  pro- 
prius). — This  is  made  up  of  association  fibers  that  connect  dif- 
ferent segments  of  the  cord.  It  is  a  compact  strand  in  the  cornu 
commissural  field  of  Marie  (Figs.  142  and  143). 

The  cornu  commissural  tract  (Fig.  143)  is  placed  between 
the  posterior  columna  (cornu),  the  posterior  commissure  and 
the  posterior  septum.  It  extends  throughout  the  spinal  cord, 
but  is  best  developed  in  the  lumbo-sacral  segments.  It  con- 
tains both  ascending  and  descending  fibers  as  do  other  parts  of 
the  fasciculus  proprius. 

Lesions  in  the  posterior  columns  cause  disturbances  of  the 
muscular  and  tactile  senses,  and  ataxia  and  incoordination  re- 
sult. If  the  entry  zone  is  involved  there  is  disturbance  of  all 
kinds  of  common  sensation,  at  the  level  of  the  lesion.  These 
columns  are  usually  involved  by  extension  from  the  posterior 
roots  in  locomotor  ataxia  (posterior  sclerosis),  hence  the  paraes- 
thesia,  crises,  loss  of  reflexes,  disturbed  equilibrium  and  ataxic 
gait. 

ROOTS  OF  THE  SPINAL  NERVES 

Thirty-one  pairs  of  spinal  nerves  connect  the  cord  with  the 
periphery.  Each  nerve  is  joined  to  the  cord  by  two  roots:  an 
anterior,  ejfferent  or  motor  root  and  a  posterior,  afferent  or  sensory 
root  (Figs.  138  and  146).  These  roots  descend  more  or  less  from 
their  cord  attachment  to  the  inter-vertebral  foramen  in  which 
they  unite  to  form  the  spinal  nerve.  The  roots  of  the  first 
cervical  nerve  are  horizontal;  those  of  the  first  thoracic  nerve 


LOWER  MOTOR  NEURONES  419 

descend  the  width  of  two  vertebrae,  and  those  of  the  twelfth 
thoracic,  the  width  of  four  vertebrae;  while  the  roots  of  the  coc- 
cygeal nerve  extend  from  the  j&rst  lumbar  vertebra  to  the  second 
piece  of  the  coccyx,  through  ten  vertebrae. 

Anterior  Root. — In  all  spinal  nerves,  except  the  first,  the 
anterior  root  {radix  anterior)  is  smaller  than  the  posterior.  It  is 
composed  of  from  four  to  six  fasciculi,  which  soon  combine  into 
two  bundles.  After  piercing  the  dura  mater,  the  anterior  root 
unites  with  the  posterior,  beyond  the  latter's  ganglion,  and 
forms  a  spinal  nerve.  The  anterior  root  is  eferentj  or  motor, 
in  function. 

Point  of  Exit  (Fig.  146). — The  anterior  root  is  composed 
of  medullated  axones  which  issue  from  the  narrow  longitudinal 
area  at  the  junction  of  the  anterior  one-fourth  with  the  posterior 
three-fourths  of  the  cord's  surface.  This  area  is  bounded  later- 
ally by  the  anterior  root-line,  commonly  called  the  anterior 
lateral  sulcus. 

Origin  (Fig.  146). — These  medullated  axones  rise  from  the 
medial,  lateral,  and  intermedio-lateral  columns  of  cell-bodies 
on  the  same  side  of  the  cord  and  from  the  medial  column  of  the 
opposite  side.  These  cell-bodies  of  the  anterior  columnae  and 
the  intermedio-lateral  column  constitute  the  genetic  nuclei 
{nuclei  origines)  of  the  spinal  nerves.  The  fibers  of  large  caliber 
in  the  anterior  roots  rise  from  the  cell-bodies  in  the  anterior 
columnae,  the  somatic  nucleus.  They  are  voluntary  motor  fibers. 
In  the  intermedio-lateral  column,  which  is  the  visceral  nucleus , 
the  small  fibers  of  the  anterior  roots  take  their  origin.  They  are 
probably  sympathetic  in  function^  that  is,  involuntary  motor, 
vasomotor,  viscero-motor,  inhibitory,  secretory,  trophic,  in- 
hibito-secretory,  and  inhibito-trophic. 

Lesions. — The  lower  motor  neurones  (spinal  and  cerebral) 
are  probably  in  a  state  of  toxic  irritation  in  laryngismus  stridu- 
lus, tetanus,  acute  ascending  paralysis  (Landry),  strychnine 
poisoning,  etc.,  hence  the  twitchings,  spasms  and  convulsions. 
Their  sudden  destruction  causes  flaccid  paralysis  (lower  seg- 
ment paralysis).  Gradual  degeneration  of  the  lower  motor 
neurones  causes  muscular  atrophy  and  slowly  increasing  paraly- 


420  THE    SPINAL    CORD  . 

sis.     In  spinal  meningitis  both  the  anterior  and  posterior  roots 
are  affected. 

The  posterior  root  {radix  posterior)  is  the  sensory,  or  afferent 
root  (Figs.  138  and  146).  It  is  larger  than  the  anterior  root, 
except  in  the  case  of  the  first  cervical  nerve;  and  is  composed  of 
from  six  to  eight  fasciculi,  which  combine  at  once  into  two 
bundles.  The  posterior  root  pierces  the  dura  mater  separately 
from  the  anterior  root.  It  unites  with  the  anterior  root  in  the 
intervertebral  foramen.  Near  the  outer  end,  it  presents  a 
swelling  which  contains  large  vesicular  bipolar  cell-bodies  and  is 
called  a  spinal  ganglion  {ganglion  spinale) .  The  ganglion  (Figs. 
138  and  146)  and  posterior  root  are  occasionally  absent  on  the 
first  nerve.  The  posterior  root,  lateral  to  the  ganglion,  is  made 
up  of  the  dendritic  processes  (Cajal)  of  the  ganglion  cells. 
These  dendrites,  which  in  appearance  are  axones,  extend  to  the 
most  distant  parts  of  the  body;  they  are  the  sensory  fibers  of 
the  spinal  nerves.  On  the  proximal  side  of  the  ganglion,  the 
posterior  root  is  composed  of  axones,  which  rise  from  the 
ganglion  cells.  Both  the  axonic  and  dendritic  processes  may 
be  medullated. 

Entrance  into  Cord  (Fig.  146). — The  posterior  roots  of  the 
spinal  nerves  enter  the  posterior-lateral  sulcus;  and,  at  once, 
divide  into  an  outer  set  of  small  fibers  and  an  inner  set  of  large 
fibers  with  some  small  ones  interspersed.  The  fibers  of  each 
set  bifurcate  into  a  large  ascending  and  a  small  descending  branch. 
Collaterals  rise  from  the  parent  axone  and  from  both  branches. 
Central  Termination  and  Terminal  Nuclei  (Fig.  146). — The 
ascending  divisions  of  the  outer  set  of  fibers  run  a  short  distance 
within  the  apex  of  the  posterior  columna,  and  end  in  ramifica- 
tions about  the  cell-bodies  of  the  substantia  gelatinosa.  They 
form  the  marginal  tract  (of  Lissauer).  Probably  their  de- 
scending branches  have  the  same  ending.  The  T-branches  and 
collaterals  of  the  inner  set  of  fibers  from  the  posterior  root  run: 
(i)  To  the  gray  matter  of  the  cord,  viz. :  To  all  parts  of  the 
posterior  columna,  to  the  center  of  the  crescent,  and  to  the 
anterior  columna  on  the  same  side.  These  fibers  end  in  relation 
with  the  dendrites  or  cell-bodies  situated  in  those  several  regions 


SPINAL   GANGLIA  42 1 

of  the  crescent  at  various  levels:  (a)  At  the  same  level  as  the 
nerve,  (b)  at  a  lower  level  than  the  nerve,  through  the  descend- 
ing radicular  tracts,  and  (c)  at  a  higher  level,  through  the  col- 
laterals given  off  by  the  ascending  tracts.  (2)  The  large 
ascending  T-branches  of  the  inner  set  of  fibers  run  to  the  medulla 
oblongata.  They  form  the  fasciculus  gracilis  and  fasciculus 
cuneatus  and  ascend  to  the  nuclei  of  those  columns  in  the 
medulla  oblongata.  They  terminate  in  the  nuclei  funiculi 
gracilis  and  cuneati.  Hence  the  terminal  nuclei  (nn.  terminales) 
of  any  spinal  nerve  are  composed  of  the  gray  crescent  of  the 
cord,  chiefly  at  the  same  level,  and  of  the  nucleus  funiculi 
gracilis  or  the  nucleus  funiculi  cuneati  in  the  medulla.  All  these 
are  somatic  terminal  nuclei^  except  the  nucleus  dorsalis  of  Clark; 
that  is  a  visceral  terminal  nucleus.  Like  other  nuclei  of  the  kind, 
it  receives  non-sensory  impulses  which  excite  reflexes,  and  it 
belongs  io  the  ajfferent  side  of  the  sympathetic  system.  Such  im- 
pulses do  not  reach  consciousness  normally;  but  under  powerful 
stimuli,  they  may  overflow  their  proper  bounds  and  pass  through 
the  cerebellum  to  the  centers  of  the  cerebrum. 

Spinal  Ganglia  {ganglia  spinalia) . — On  the  posterior  root  of 
every  spinal  nerve,  with  the  possible  exception  of  the  first 
cervical,  there  is  a  fusiform  swelling,  4—6  mm.  long,  called  a 
spinal  ganglion.  The  spinal  ganglia  are  often  bifurcated  at  the 
proximal  end,  where  they  are  continuous  with  the  two  fasciculi 
of  the  posterior  root.  They  lie  upon  the  neural  arches  of  the 
first  two  vertebrae;  but,  below  that,  are  located  in  the  interverte- 
bral foramina,  down  to  the  last  lumbar  nerve.  The  ganglia  of 
the  sacral  and  coccygeal  nerves  are  within  the  vertebral  canal; 
but,  excepting  the  last,  are  outside  the  dural  sheath.  The 
ganglia  in  man  are  composed  of  pear-shaped,  bipolar  cell-bodies 
with  their  processes  and  nucleated  capsules.  Dogiel  also  de- 
scribes typical  multipolar  cells  (sympathetic  neurones)  in  spinal 
ganglia,  and  they  are  undoubtedly  present  in  the  mixed  cranial 
ganglia  (geniculate  of  the  seventh,  petrosal  of  the  ninth,  and 
jugular  of  the  tenth) ;  but  recent  studies  have  not  shown  them  in 
purely  sensory  ganglia.  The  cell-bodies  vary  in  size  from  25- 
170/i,  the  greater  number  measure  from  60-80/^  in  their  long  axis. 


422  THE    SPINAL   CORD 

Each  cell  contains  a  large  spherical  nucleus,  with  one  or  more 
nucleoli,  and  possesses  all  the  cytoplasmic  constituents  common 
to  neurones  (p.  169).  The  axone  hillock  is  well  developed 
and  from  it  originates  the  single  composite  process,  formed  by  the 
approximation  of  axone  and  dendrite.  This  composite  process, 
constituting  the  stem  of  the  pear-shaped  cell,  pursues  a  tortuous 
course  of  variable  length,  sometimes  equaling  three  or  four  times 
the  diameter  of  the  cell-body;  it  then  separates  into  its  compo- 
nent axone  and  dendrite  which  continue  in  opposite  directions, 
the  dendrite  toward  the  periphery  and  the  axone  into  the  cord 
as  a  posterior  root-fiber.  The  dendrites  are  the  larger  processes, 
though  many  of  them  are  non-medullated.  The  caliber  of  the 
axones  is  proportionate  to  the  size  of  the  cell-bodies  from  which 
they  arise :  about  one-third  of  them  are  large  and  are  medullated; 
two-thirds  are  small  or  of  medium  size  and  most  of  them  are  non- 
medullated  (Ranson).  As  the  axones  enter  the  cord,  through 
the  posterior  lateral  sulcus,  they  fall  into  two  strands,  a  medial 
and  a  lateral.  The  lateral  bundle,  made  up  of  fine  non-medullated 
fibers,  with  a  few  medullated  fibers  of  medium  size,  enters 
the  apex  of  the  posterior  columna,  where  its  fibers  divide 
T-like  and  form  the  marginal  tract  of  Lissauer.  The  medial 
bundle  is  composed  of  the  large  medullated  fibers  and  of  a  con- 
siderable number  of  small  and  medium  sized  fibers,  some  of 
which  possess  a  myelin  sheath.  The  small  and  medium  fibers 
end  quickly  in  the  gray  crescent  above  and  below  the  point  of 
entrance;  the  large  fibers  terminate  chiefly  in  the  dorsal  nucleus 
of  the  cord  and  the  nucleus  gracilis  and  nucleus  cuneatus  of  the 
medulla,  their  descending  rami  terminate  in  segments  of  the 
cord  below  the  points  of  entrance. 

Besides  the  single  composite  process  given  off  by  the  spinal 
ganglion  neurones,  many  investigators  have  observed  accessory 
processes  which  end  in  the  form  of  points  or  bulbs  within  the 
capsule  of  the  cell;  and  protoplasmic  loops  and  plexuses  continu-. 
ous  with  the  cytoplasm  of  the  cell  which,  likewise,  are  contained 
within  the  capsule.  These  are  not  permanent  formations;  they 
change  quickly  and  may  disappear  entirely.  They  are  found 
during  development  and  under  conditions  of  stimulation,  par- 


COMBINED   CONDUCTION  423 

ticularly,  and  are  probably  the  result  of  amoeboid  movement. 
Dogiel  may  have  mistaken  the  accessory  processes  for  the 
dendrites  of  a  multipolar  cell. 

The  nucleated  capsule  of  each  cell  in  a  spinal  ganglion  is  con- 
tinuous with  the  neurolemma  of  its  processes;  it  invests  the 
whole  neurone  from  the  surface  of  the  spinal  cord  to  a  point  near 
the  end- tufts  of  its  dendrites;  and  it  incloses  a  lymph  space  in 
which,  according  to  Orr  and  Rows,  there  is  a  centripetal  current 
flowing  into  the  spaces  of  the  cord  and  its  membranes. 

Spinal  ganglion  neurones  carry  all  kinds  of  common  sensory 
impulses,  in  harmony  with  the  law  that  jirst  order  common 
sensory  neurones  conduct  impulses  in  combinations;  second 
order  common  sensory  neurones  form  specific  paths  each  of 
which  conveys  only  one  variety  of  impulse.  Hence,  lesion  of 
the  posterior  column  of  the  cord,  not  involving  the  nerve  roots, 
causes  more  or  less  loss  of  a  whole  group  of  sensations — as 
muscle-sense,  tactile  discrimination,  sense  of  size,  shape  and 
form,  of  weight,  of  vibration,  etc. ;  while  localized  lesions  of  the 
lateral  column  of  the  cord  may  produce  the  loss  of  a  single  variety 
of  common  sensation — as  pain,  heat,  cold,  or  tactile  localiza- 
tion— without  affecting  any  others  conducted  by  the  lateral 
column.  ~^ 

Physiologically,  we  may  divide  the  fibers  of  the  posterior 
roots  of  the  spinal  nerves  into  four  groups,  viz.;  i.  Spinal 
rejlex  fibers,  which  end  within  the  gray  crescent  on  the  same 
side,  above  and  below  the  point  of  entrance,  and  excite  simple 
reflexes,  2.  Cerebellar  reflex  fibers;  they  terminate  in  relation 
with  the  neurones  that  form  the  dorsal  and  ventral  spino-cere- 
bellar  tracts,  and  they  excite  coordinated  reflexes  in  the  cere- 
bellar cortex.  Both  these  groups  (i  and  2)  carry  non-sensory 
impulses.  The  two  groups  following  (3  and  4)  convey  their 
impulses  to  consciousness;  their  impulses  result  in  sensations. 
3.  Fibers  that  form  the  fasciculus  gracilis  and  fasciculus  cuneatus 
and  terminate  in  the  nuclei  of  those  tracts.  This  group  con- 
ducts impulses  of  the  muscle-sense,  impulses  leading  to  tactile 
discrimination  and  to  recognition  of  size,  shape,  form  in  three 
dimensions,  of  vibration,  of  weight,  etc.     Such  impulses  come 


424  THE    SPINAL   CORD 

from  muscles,  tendons,  joint  surfaces,  skin  and  mucous  mem- 
branes. 4.  Fibers  that  end  within  the  gray  matter  in  relation  with 
the  origin  of  the  spino -thalamic  tract.  Through  the  fibers  of  this 
group  pass  impulses  of  pain,  heat,  cold,  and  tactile  localization, 
which  arise  largely  in  the  skin  and  mucous  membranes  but  also 
in  the  deep  structures. 

Impulses  due  to  light  touch  and  to  pressure  travel  a  direct 
path  up  the  posterior  column  and  a  crossed  path  up  the  lateral 
column. 

Lesions. — The  posterior  roots  of  the  spinal  nerves  and  the 
spinal  ganglia  are  affected  in  locomotor  ataxia,  and  the  lesion 
extends  to  the  marginal  tract  (of  Lissauer)  and  the  posterior  col- 
umn of  the  cord.  Excepting  the  fasciculus  proprius,  the  whole 
posterior  column  becomes  involved.  The  spinal  ganglia  are  the 
seat  of  specific  inflammation  in  herpes  zoster. 

As  stated  above,  peripheral  common  sensory  nerves  conduct  impulses  in 
combinations,  but  every  fiber  is  not  capable  of  conducting  all  varieties  of 
common  sensory  impulse.  The  work  of  Head,  Rivers  and  Sherren,  and  of 
Sherrington  (Brain,  Vol.  28  and  Vol.  29)  show  that  common  afferent 
nerves  form  four  great  systems  which  are  physiologically  distinct  and 
probably  are  evolved  at  different  phylogenetic  periods.  These  systems 
are  as  follows: 

1.  The  proprio-ceptors,  the  mechanism  of  deep  sensibility. 

2.  The  protopathic  extero-ceptors,  and 

3.  The  epicritic  extero-ceptors. 

The  extero-ceptors  are  the  nerves  of  cutaneous  sensibility,  etc. 

4.  The  intero-ceptors,  the  afferent  nerves  of  the  internal  organs — • 
the  alimentary  tract,  the  respiratory  tract,  the  genito-urinary  tract, 
etc.,  excepting  the  regions  near  the  external  orifices. 

I.  The  system  belonging  to  deep  sensibility,  the  proprio-ceptors,  com- 
prises the  nerves  that  supply  muscles,  tendons,  ligaments  and  joint  surfaces, 
and  the  vestibule  and  semicircular  canals  of  the  labyrinth.  The  proprio- 
ceptors respond  to  such  stimuli  as  tension,  pressure,  posture  and  move- 
ment; and  to  painful  stimuli  due  to  excessive  pressure  or  to  pathologic 
condition  of  muscle,  tendon,  joint,  etc.  They  enable  the  individual 
to  locate  the  point  of  stimulation,  to  determine  the  drection  of  move- 
ment and  the  posture  of  any  part.  The  common  proprio-ceptors  con- 
stitute the  peripheral  mechanism  of  the  muscle-sense,  plus  a  part  of 
the  mechanisms  of  tactile  localization  and  pain.  The  vestibular  nerve 
is  a  special  proprio-ceptor.    As  all  stimuli  of  the  proprio-ceptors,  with 


FOUR   SYSTEMS   OF   AFFERENT   NERVES  425 

the  single  exception  of  pressure,  originate  within  the  organism^  this  system 
of  nerves  is  called  by  Sherrington  the  "proprio-ceptors."  The  impulses 
conducted  by  this  system  set  up  important  reflexes;  but  most  of  them 
fail  to  reach  consciousness. 

The  extero-ceptors  are  the  nerves  of  the  skin  and  the  adjacent  parts 
of  mucous  membranes;  also  the  nerves  of  the  special  senses — taste,  smell, 
sight  and  hearing  (not  equilibrium).  These  nerves  are  stimulated  by 
environment,  hence  the  nerves  adapted  to  receive  stimuli  from  without 
the  organism  are  called  the  "extero-ceptors."  The  extero-ceptors  may 
be  divided  into  a  distance  and  a  contact  subgroup.  The  nerves  of  sight 
and  hearing  are  the  distance  extero-ceptors,  as  through  them  we  appear 
to  perceive  things  at  a  distance.  But  in  reality  they  are  contact  receptors, 
because  they  respond  only  to  the  air  and  ether  vibrations  that  reach  their 
end-organs. 

2.  The  protopathic  extero-ceptors  constitute  a  primitive  system  of 
afferent  nerves,  probably  of  great  phylogenetic  age.  They  are  con- 
nected with  specific  "pain  spots,"  "cold  spots"  and  "heat  spots"  of 
the  skin  and  mucous  membranes  (near  the  external  orifices).  Con- 
sequently, this  system  responds  to  painful  cutaneous  stimuli  and  to  ex- 
treme degrees  of  cold  (below  26°  C.)  and  heat  (above  37°  C).  The 
system  possesses  three  specific  end-organs — for  pain,  cold  and  heat — 
and  each  is  incapable  of  responding  to  any  other  kind  of  stimulus.  The 
sensations  excited  through  the  protopathic  system  are  intense,  diffuse 
and  non-localized;  the  point  stimulated  cannot  be  determined  and  false 
reference  to  some  other  part  is  characteristic  of  it.  Light  touch,  warmth 
and  coolness  are  ineffective  stimuli  of  this  system,  they  excite  no  response. 
Protopathic  impulses  produce  their  appropriate  sensation  and  also 
excite  reflexes.  The  connection  of  the  protopathic  extero-ceptors  with 
the  spinal  cord  is  distinctly  segmental;  this  is  another  evidence  of  its 
primitive  character. 

3.  The  Epicritic  Extero-ceptors. — This  critical  and  discriminating  system 
of  cutaneous  nerves  develops  later  in  phylogenetic  history  than  the  pro- 
topathic system,  if  we  may  judge  from  its  regeneration  after  experimental 
section  (as  the  superficial  radial  nerve  in  the  arm  of  Henry  Head).  The 
epicritic  system  responds  to  light  touch;  to  warmth,  between  34°  and  37° 
C.  and  to  coolness,  between  26°  and  29°  C.  It  enables  one  to  locate  the 
exact  point  stimulated  (tactile  localization),  to  distinguish  two  or  more 
points  of  simultaneous  contact  (tactile  discrimination),  and  to  recognize 
size,  shape  and  form  (stereognosis) .  The  connection  of  the  roots  of 
this  system  with  the  spinal  cord  is  very  loosely  segmental,  its  root-fibers 
spread  widely  above  and  below  the  segment  to  which  the  nerve  properly 
belongs.  The  activity  of  the  epicritic  extero-ceptors  exercises  a  regulating 
and  inhibiting  influence  over  the  protopathic  system;  it  abolishes  vividness, 


426  THE   SPINAL   CORD 

radiation  and  false  reference  and  thus  greatly  reduces  the  intensity  of 
pain  without  raising  its  threshold. 

4.  The  inter o-ceptors  include  the  afferent  nerves  supplying  the  internal 
organs — the  aHmentary,  respiratory  and  genito-urinary  tracts.  Near 
the  external  orifices  the  protopathic  and  epicritic  systems  are  distributed 
as  in  the  lips,  tongue,  throat,  larynx,  upper  part  of  the  oesophagus  and 
lower  part  of  the  rectum.  The  intero-ceptors  form  the  afferent  side  of 
a  great  reflex  system;  few  of  their  impulses  pass  over  the  threshold  of 
consciousness.  The  work  of  Hertz  on  "The  Sensibility  of  the  Alimentary 
Tract"  throws  much  light  on  this  subject.  All  internal  organs  are 
insensitive  to  tactile  stimuli  and,  excepting  the  oesophagus  and  anal 
canal,  they  are  insensitive  to  cold  and  heat  stimuli.  The  stomach  and 
intestines  are  responsive  to  stimulation  with  alcohol,  but  not  to  dilute 
mineral  and  organic  acids.  The  intero-ceptors  are  very  responsive 
to  tension;  under  normal  conditions,  tension  is  the  only  stimtdus  of  the 
intero-ceptors  that  gives  rise  to  pain. 

These  four  systems  of  peripheral  neurones  carry  their  proper  impulses 
into  the  cerebrospinal  axis  in  as  many  combinations;  but,  when  the 
second  order  neurones  are  reached,  the  impulses  are  re-grouped  and  all 
of  the  same  variety  traverse  one  specific  path,  in  obedience  to  Sherrington's 
law  of  integration.  Then,  impulses  of  light  and  deep  touch  flow  in  one 
path;  pain  impulses  from  the  protopathic  extero-ceptors,  the  intero-ceptors 
and  deep  systems  flow  through  one  path;  impulses  due  to  coolness  (26° 
to  29°  C.)  and  to  cold  (anything  below  26°  C.)  traverse  one  separate  path; 
impulses  produced  by  warmth  (34°  to  37°  C.)  and  by  high  heat  (above 
37°  C.)  journey  in  one  special  path  and  localizing  impulses  from  the 
epicritic  and  deep  mechanisms  travel  the  same  specific  path. 


CHAPTER  VII 
TRACING  OF  IMPULSES 

Having  studied  the  grouping  and  chaining  together  of  neu- 
rones, let  us  now  make  the  knowledge  practical  by  tracing  im- 
pulses through  the  better  known  paths  formed  by  these  various 
neurone  groups.  The  paths  thus  formed  are  of  three  kinds, 
namely:  I.  Efferent,  or  motor.  11.  Afferent,  or  sensory — 
general  and  special  sense.     III.  Reflex. 

The  nerve  impulse  resembles  the  electric  current,  in  that  it 
deflects  the  needle  of  the  galvanometer,  but  it  travels  at  a  much 
slower  speed.  It  was  once  considered  to  be  ''animal  spirits'' 
and  later  ''nerve  juice"  which  flowed  through  the  "tubular" 
nerves.  Galvani  first  suspected  its  electric  character  in  1786, 
when  he  accidentally  obtained  contraction  of  a  leg  muscle  upon 
connecting  a  lumbar  nerve  with  it  by  means  of  a  copper-and-iron 
circuit.  The  glory  of  measuring  the  velocity  of  the  nerve 
impulse  belongs  to  Helmholtz.  In  1852,  using  the  motor  nerve 
of  a  frog,  he  found  the  speed  to  vary  between  24  and  38  m.  per 
sec.  It  is  said  by  S.  Weir  Mitchell  to  be  more  rapid  in  sensory 
nerves ;  31  m.  per  sec.  in  an  efferent  nerve  and  47  m.  per  sec.  in  an 
afferent  nerve.  The  rate  is  slower  in  lower  animals  than  in  man. 
In  the  amoeba  it  is  but  0.93  m.  per  sec.  (Mitchell).  Piper,  in 
1908,  estimated  the  rate  in  man  at  125  m.  per  sec. 

I.    EFFERENT,  OR  MOTOR  PATHS 

The  cerebrospinal  or  pyramidal  paths  (Fig.  147)  are  direct, 
as  they  do  not  pass  through  the  cerebellum.  Their  impulses 
ultimately  run  either  through  the  spinal  or  the  cerebral  nerves, 
and  are  both  motor  and  inhibitory.  Hence  the  increased 
reflexes  and  spastic  contractions  of  lateral  sclerosis  in  which 
these  tracts  are  diseased. 

427 


428 


TRACING   OF   IMPULSES 


fillet  (Bechterewi) 
to  nuclei  of  cerebral  nerves 


Nucleus  pontis 


Medulla 


Anterior 
pyramidal  tract 


Pyramid 


Pyramidal  decussation 
Lateral  pyramidal 


Cord 


Anterior  root  of  spinal  nerve 

Fig.  149. — Direct  motor  paths  from  cerebral  cortex,  to  cerebral  and  spinal 
nerves.     Diagrammatic.     (Original.) 

Motor  paths  extending  from  the  cortex  of  the  anterior  central  gyrus  to  the  nuclei  of  the 
motor  cerebral  nerves  and  of  the  anterior  roots  of  the  spinal  nerves;  O.  represents  point 
where  the  section  is  pierced  by  a  longitudinal  fiber;  3,  4,  5,  6,  7.  9.  10,  11,  and  12,  nuclei  of 
cerebral  nerves. 


MOTOR  PATHS  429 

1.  Through  the  Spinal  Nerves  (Fig.  147). — Starting  in  the 
upper  three-fourths  of  the  gyrus  centraHs  anterior  of  the  cerebral 
cortex,  motor  and  inhibitory  impulses  run  down  through  the 
corona  radiata,  the  anterior  two-thirds  of  the  occipital  part  of 
the  internal  capsule,  the  middle  three-fifths  of  the  basis  pedun- 
culi,  the  basilar  longitudinal  fibers  of  the  pons,  and  the  pyramid 
of  the  medulla  oblongata,  whence  they  proceed  by  the  lateral 
and  anterior  pyramidal  tracts  to  the  gray  crescent,  partly  in  the 
same  side  but  chiefly  in  the  opposite  side  of  the  spinal  cord.  By 
the  former  route,  the  impulses  cross  over  in  the  medulla,  through 
the  decussation  of  the  pyramids,  and  descend  in  the  lateral 
column  of  the  spinal  cord  to  the  gray  substance  in  the  vicinity  of 
the  nucleus  dorsalis  (Clarki),  where  the  path  is  relayed,  and 
intrinsic  neurones  carry  the  impulses  forward  into  the  anterior 
columna;  but  by  the  anterior  route,  they  descend  in  the  anterior 
column  of  the  cord  and  decussate,  in  succession,  through  the 
white  anterior  commissure.  Impulses  by  either  route  finally 
reach  the  anterior  gray  columna  of  the  spinal  cord  and,  with  the 
exception  of  a  small  per  cent,  of  them,  they  reach  the  columna 
opposite  to  their  cortical  origin.  The  few  undecussated  fibers  in 
the  lateral  pyramidal  tract  conduct  uncrossed  impulses  to  the 
anterior  columna  of  the  same  side.  Thus  are  explained  two 
symptoms  of  hemiplegia  due  to  cerebral  lesion,  viz.,  weakness  on 
the  well  side  and  slight  motion  on  the  paralyzed  side.  From  the 
anterior  gray  columna  of  the  spinal  cord  the  nerve  commotions 
are  conducted  by  the  efferent,  or  motor  fibers  of  the  spinal  nerves 
to  the  muscles. 

2.  Through  the  Cerebral  Nerves  (Fig.  147). — Impulses  des- 
tined to  the  cerebral  nerves  run  chiefly  from  the  lower  two- 
fourths  of  the  anterior  central  gyrus  through  corona  radiata, 
genu  of  internal  capsule  and  on,  by  the  same  path  as  the  im- 
pulses to  spinal  nerves,  down  to  the  point  where  they  leave  the 
pyramidal  tract  to  enter  the  nuclei  of  the  cerebral  nerves,  which 
some  of  them  do  in  the  vicinity  of  the  several  nuclei.  According 
to  Bechterew  they  run,  at  least  in  part,  through  pyramidal 
fibers  which  constitute  the  accessory  lemniscus.  These  fibers 
leave  the  pyramidal  tract  near  the  internal  capsule,  and  descend 


430  TRACING   OF  IMPULSES 

through  the  medial  portion  of  the  fillet  to  points  near  the  respect- 
ive nuclei  in  which  they  end  by  multiple  division.  From  either 
hemisphere  impulses  proceed  to  the  nuclei  of  both  sides.  But 
the  greater  number  enter  the  nucleus  of  the  fourth  nerve  on  the 
same  side,  and  the  nuclei  of  the  third,  fifth,  sixth,  seventh,  ninth, 
tenth,  eleventh  and  twelfth  cerebral  nerves  of  the  opposite  side. 
By  the  above  nine  nerves  innervation  is  conducted  to  the  mus- 
cles of  the  orbit;  the  muscles  of  mastication  and  expression; 
the  muscles  of  the  tongue,  palate  and  ear;  the  digastric  and 
styloid  muscles;  the  muscles  of  the  larynx,  trachea  and  bronchi, 
and  of  the  pharynx,  espohagus,  stomach,  and  the  intestines 
down  to  the  descending  colon.  And  inhibitory  impulses  are 
carried  to  the  heart;  also  vasodilator,  secretory,  trophic  and 
inhibito-secretory  impulses  to  alimentary  glands,  etc. 

The  Cerebro-pontal  Paths,  Frontal,  Temporal  and  Inter- 
mediate.— These  paths  are  indirect  for  spinal  nerves  since  they 
run  through  the  cerebellum. 

Fronto-pontal  (Fig.  148). — The  impulses  originate  in  the  pre- 
frontal region  and  descend  through  corona  radiata,  the  frontal 
part  of  the  internal  capsule,  and  the  medial  fifth  of  the  basis 
pedunculi  to  the  nucleus  pontis.  Temporo-pontal. — They  rise 
in  the  temporal  cortex  and  run  through  corona  radiata,  the 
occipital  part  and  inferior  lamina  of  the  internal  capsule,  and  the 
lateral  fifth  of  the  basis  pedunculi  to  the  nucleus  pontis.  Inter- 
mediate Bundle.- — Cortical  impulses  of  unknown  origin  are 
received  by  the  corpus  striatum,  by  way  of  the  thalamus  and 
conveyed  by  a  bundle  of  strio-fugal  axones  which  form  the  deep 
portion  of  the  basis  pedunculi,  to  the  substantia  nigra  and  then 
to  the  nucleus  pontis,  chiefly  of  the  same  side.  The  impulses 
thus  traverse  the  internal  capsule  and  a  broad  but  thin  area  in 
the  basis  pedunculi  just  ventral  to  the  substantia  nigra  and 
dorsal  to  the  pyramidal  tract.  In  all  three  of  these  paths  the 
impulses  run  to  the  nucleus  pontis  of  the  same  side  and  to  motor 
nuclei  of  the  cerebral  nerves.  Whence  they  proceed  from 
nucleus  pontis:  {i)  To  Spinal  Nerves.  They  run  through  the 
brachium  pontis  to  the  cerebellar  cortex  and  thence  continue 
(a)  down  a  cerebello-spinal  path  to  the  anterior  gray  columna  of 


INDIRECT  EFFERENT  PATHS 


431 


Fibersjrom  red-nucleus 
to  nucleus  dentatus 


Temporo-pontal  tract 
Intermediate  tract 
Fronto-Pontal  tract 


Nucleus  pontis  containing  end- 
ings of  cerebro-pontal  tracts 
and  origin  of  brachium  pontis 

Vestibulo-spinal  tract 


Medulla 


Rubro-spinal  tract 


Cord 


"99 


Anterior  root  of  spinal  nerve 
Fig.  150. — Indirect  e£ferent  paths  to  the  spinal  nerves.     Diagrammatic. 

(Original.) 

Motor  paths  frorn  cerebral  cortex  through  the  cerebellum  to  spinal  nerves.  A.  Fronto- 
pontal  tract  rising  in  frontal  lobe.  B.  Intermediate  tract  rising  in  lentiform  nucleus.  C. 
Temporo-pontal  tract  rising  in  middle  and  inferior  temporal  gyn.  Also  rubro-spinal  tract. 
O  O  represent  points  of  perforation  in  the  sections. 


432  TRACING   or   IMPULSES 

the  spinal  cord.  Their  course  from  the  cerebellar  cortex  is 
through  the  cor tico-nu clear  neurones  of  Purkinje,  to  nucleus 
fastigii;  the  fastigio-bulbar  fibers,  to  nucleus  of  Deiters  in  the 
medulla;  and  the  vestibulo-spinal  tract,  to  the  anterior  columna 
of  the  spinal  cord.  (6)  Again,  from  the  cerebellar  cortex  these 
impulses  reach  the  cord  via  the  red  nucleus  and  thalamus. 
They  are  conducted  in  succession  by  the  following  neurones — 
Purkinje's  cortico-nuclear  neurones,  to  nuclei  dentatus  and 
emboliformis;  the  cerebello-tegmental  neurones,  to  opposite 
red  nucleus  and  thalamus  through  the  brachium  conjunctivum; 
and  the  rubro-spinal  and  thalamo-spinal  neurones,  to  the  ante- 
rior columna  of  the  cord.  From  the  gray  matter  of  the  spinal 
cord  the  impulses  are  conveyed  by  the  motor  fibers  of  the  spinal 
nerves  to  the  muscles  which  they  supply.  -(2)  To  Cerebral 
Nerves.  The  impulses  run  from  synapses  formed  in  the  cere- 
bral nuclei,  by  the  fibers  of  the  cerebro-pontal  tracts,  through 
the  motor  fibers  of  these  nerves  to  their  distribution.  These 
impulses  also  reach  cranial  nerve  nuclei  by  the  indirect  route 
through  the  cerebellum.  The  cortico-nuclear  fibers,  and  the 
cerebello-tegmental  fibers,  in  the  brachium  conjunctivum  and 
restiform  body,  connect  the  cerebellar  cortex  with  the  motor 
nuclei  of  cranial  nerves.  Certain  fibers  of  rubro-spinal  and 
thalamo-spinal  tracts  also  end  in  these  nuclei. 

The  efferent  impulses  of  the  cerebro-pontal  tracts  are  evi- 
dently not  voluntary  motor;  they  probably  regulate  and  coor- 
dinate the  functions  of  the  lower  motor  neurones. 

Paths  Through  the  Red  Nucleus  (Fig.  148)  .^Impulses  run 
from  the  opercular  part  of  the  cerebral  cortex  in  the  frontal  lobe 
to  the  red  nucleus.  From  the  red  nucleus  they  pursue  a  direct 
route  to  motor  nuclei,  cranial  and  spinal. 

The  Rubro-spinal  Path. — By  this  route,  impulses  run  through 
the  crossed  descending  tract  of  the  red  nucleus  to  the  cerebral 
nuclei  and  gray  crescent  in  the  opposite  side  of  the  spinal  cord. 
Crossing  the  median  raphe  at  once,  in  the  hypothalamic  region 
through  the  ventral  tegmental  decussation  (Foreli),  the  im- 
pulses descend  by  way  of  the  rubro-spinal  tract,  through  the  ven- 
tral part  of  the  formatio  reticularis  of  the  mid -brain  and  pons,  in 


THALAMO   AND   RETICULO-SPINAL  PATHS  433 

the  medial  part  of  the  lateral  fillet,  then  through  the  lateral 
column  of  the  medulla,  among  the  fibers  of  the  ventral  spino- 
cerebellar tract,  and  finally  down  the  spinal  cord,  through  the 
field  ventral  to  the  lateral  pyramidal  tract,  to  their  destina- 
tion in  the  gray  matter.  From  the  gray  crescent  they  proceed, 
with  or  without  transferring,  to  the  root  neurones  of  the  spinal 
nerves  and  are  conducted  to  the  muscles. 

The  red  nucleus  is  also  a  very  important  station  in  the  coor- 
dinating reflex  arc  concerned  with  locomotion  (Horsley). 

Paths  Through  the  Thalamus. — The  thalamus  is  a  center  oj 
consciousness  for  the  impulses  of  pain  and  temperature  (Head  and 
Holmes)  and  it  receives  impulses  from  many  parts  of  the  cere- 
bral cortex.  Thalamic  impulses  descend  through  the  thalamo- 
spinal  tract  to  the  motor  nuclei  of  the  brain-stem  and  the  gray 
crescent  of  the  cord.  This  tract  accompanies  the  rubro-spinal 
tract;  but  whether  or  not  it  decussates  with  the  rubro-spinal 
tract  is  at  present  undetermined.  Through  the  thalamus  and 
red  nucleus  two  very  important  strio-fugal  paths  reach  the 
motor  nuclei  and  convey  to  them  steadying  influences.  Again, 
the  thalamus  is  an  important  station  in  several  reflex  systems. 

Reticulo-spinal  Paths.— The  reticulo-spinal  tract  is  the 
name  suggested  for  the  tracts  originating  in  the  nuclei  of  the 
reticular  formation,  chiefly  in  the  pons,  and  descending  to  the 
gray  matter  of  the  spinal  cord.  There  are  two  of  them  on  either 
side.  The  anterior  reticulo-spinal  tract  accompanies  the  medial 
longitudinal  bundle  down  the  anterior  ground  bundle  of  the 
cord  without  decussating,  unless  the  crossing  occurs  near  the 
termination.  The  lateral  reticulo-spinal  tract  which  is  crossed 
decussates  in  the  brain  stem  near  its  origins  and  descends  in  the 
lateral  column  of  the  spinal  cord.  Just  how  the  impulses  reach 
the  nuclei  centrales  and  nuclei  laterales  of  the  formatio  reticu- 
laris, in  which  the  reticulo-spinal  tracts  take  their  origins,  cannot 
be  definitely  stated;  but,  having  arrived  in  them,  they  descend 
to  both  crescents  of  the  spinal  cord  and  apparently  enter  into  all 
its  segments.     The  anterior  nerve  roots  complete  the  paths. 

Short  Fiber  Paths. — Those  are  paths  in  the  formatio  reticu- 
laris chiefly,     (i)  Impulses  having  reached  the  great  ganglia  of 
28 


434 


TRACING   OF   IMPULSES 


Red  nucleus 
Decussation  of  brachia  conjunctiva 
Brachium  conjunctivum 


Vestibular  root 
VIII  nerve 


IX  nerve 


X  nerve 
Anterior  external  arcuate  fibers 


Dorsal,  spino-cerebellar  tract 

Fasciculus  cuneatus 

Fasciculus  gracilis 


Sacral  nerve 
Cervical  nerve 
Thoracic  nerve 


V  nerve 


Pons  and  cerebellum 


Restiform  body  containing  arcuate 
and  dorsal  spino-cerebellar    fibers 

Medial  fillet 

Nucleus  funiculi  gracilis 
Nucleus  funiculi  cuneati 


Medvdla 

Fillet  decussation 


Post.^roots 
Spinal  nerves 


Fig.  151. — Common  sensory  paths,  muscular,  tactile  and  sympathetic,  by  way 
of  the  posterior  column  and  dorsal  spino-cerebellar  tract.  Diagrammatic. 
(Original.) 

These  paths  terminate  in  the  posterior  central  gyrus  and  in  the  cerebellar  cortex. 


SHORT  FIBER  TRACTS  435 

the  cerebrum  and  mid-brain  may  run  through  many  relays  down 
the  formatio  reticularis  of  mid-brain,  pons  and  medulla  and  the 
antero-lateral  fasciculus  proprius  of  the  spinal  cord,  to  the  gray 
crescent  of  the  same,  and  continue  through  the  anterior  root- 
fibers  to  their  destination.  On  the  other  hand,  the  impulses, 
leaving  formatio  reticularis  in  mid-brain,  pons  or  medulla,  may 
enter  the  nuclei  of  motor  cerebral  nerves  and  be  conducted  by 
them  to  the  muscles  and  glands  supplied  by  cerebral  nerves. 
(2)  The  impulses  may  leave  the  formatio  reticularis  in  the  pons, 
and  run  to  the  cerebellar  cortex  through  the  brachium  pontis. 
From  the  cerebellum  they  may  follow  the  ordinary  course 
through  the  cerebello-spinal  path,  by  way  of  the  nucleus  of 
Deiters,  to  the  anterior  gray  columna  of  the  cord.  (3)  Impulses 
having  arrived  at  the  thalamus,  may  descend  the  thalamo- 
olivary  tract  to  the  inferior  olivary  nucleus  of  the  medulla  and 
pass  to  the  cerebellar  cortex  of  the  opposite  side,  through  the 
olivo-cerebellar  fibers.  The  thalamo-olivary  fasciculus  runs 
through  the  middle  of  the  tegmentum  of  mid-brain  and  pons  and 
the  lateral  column  of  the  medulla  to  the  dorso-lateral  wall  of  the 
inferior  olive;  the  olivo-cerebellar  fibers  cross  over  in  the 
medulla  to  the  opposite  restiform  body,  through  which  the  im- 
pulses reach  the  cerebellar  cortex.  Any  impulses  in  the  cortex 
of  the  cerebellum  may  pass  through  the  cortico-nuclear  fibers  to 
the  cerebellar  nuclei  and  the  cerebello- tegmental  fibers  from 
these  nuclei,  via  brachium  conjunctivum  and  restiform  body, 
directly  to  motor  cranial  nerve  nuclei;  and,  through  the  rubro- 
spinal, thalamo-spinal  and  the  vestibulo-spinal  tracts,  they  may 
continue  to  the  motor  nuclei  of  cranial  and  spinal  nerves. 
(4)  Through  certain  short  fibers  in  the  medial  longitudinal 
bundle  which  rise  in  the  nucleus  of  the  sixth  cerebral  nerve  and 
cross  to  the  opposite  nucleus  of  the  motor  oculi,  impulses  run 
from  the  nucleus  of  the  abducent  through  the  opposite  third 
nerve  to  the  internal  rectus  oculi.  They  explain  the  conjugate 
action  of  the  eyes  in  health,  and  also  the  conjugate  deviation 
observed  in  lesions  affecting  the  nucleus  of  the  sixth  nerve.  In 
nuclear  lesions  of  the  abducent  nerve  the  external  rectus  of  the 
same  eye  and  the  internal  rectus  of  the  other  eye  are  para- 


436  TRACING   OF   IMPULSES 

lyzed  if  the  nucleus  is  destroyed  and  stimulated  if  the  nucleus 
is  only  irritated. 

n.  AFFERENT,  OR  SENSORY  PATHS 

The  sensory  paths  conduct  two  varieties  of  impulses,  viz., 
general  and  special.  The  impulses  originate  in  the  end-organs 
of  the  cerebral  and  spinal  nerves  and  by  those  nerves  are  con- 
veyed to  the  cerebro-spinal  axis  through  which  they  reach  the 
proper  cortical  area  in  the  cerebrum. 

I.  General  Sensations 

General  sensation  is  the  function  of  the  sense  of  touch.  This 
sense  has  four  important  subdivisions — the  tactile  sense,  mus- 
cular sense,  pain  sense,  and  temperature  sense.  Stereognosis  is 
only  an  associated  interpretation  of  the  impulses  of  the  sense 
of  touch  and  not  a  subdivision  of  it.  Tactile  sensations  appear 
to  be  most  elemental  and,  in  the  cord  may  be  conducted  by 
the  posterior  and  lateral  columns.  Other  common  sensations 
seem  to  require  some  specialization,  as  yet  not  understood,  in 
their  conducting  media;  and  pain  and  temperature  impulses 
pursue  a  path  entirely  distinct  from  that  followed  by  impres- 
sions of  the  muscular  sense.  In  giving  the  common  sensory 
tracings,  the  following  classification  will  be  adhered  to,  though 
conclusive  evidence  of  certain  points  in  it  is  still  lacking. 

I.  Paths  conducting  impulses  of  the  muscular  and  tactile 
senses,  chiefly,  from  muscles,  tendons,  joint  surfaces,  and  the 
skin.     Spinal  and  cerebral  (Fig.  149). 

II.  Paths  conveying  pain,  temperature,  and  tactile  impulses. 
Spinal  and  cerebral  (Fig.  150). 

I.  Paths  Transmitting  Impulses  of  the  Muscular  and 
Tactile  Senses,  chiefly  from  muscles,  tendons,  ligaments, 
joint  surfaces  and  the  skin. 

Through  Posterior  Column  and  Fasciculi  Gracilis  et  Cu- 
neatus  (Fig.  149). — Impulses  originating  in  the  end-organs  of 
the  spinal  nerves  traverse  the  dendrites  of  the  spinal  ganglion 
neurones  (Cajal),  the  cell-bodies  in  the  ganglia,  and  then  the 


COMMON  AFFERENT  PATHS  437 

axones  of  the  same.  They  enter  the  cord  through  the  posterior 
roots  of  the  spinal  nerves  and  ascend  through  the  posterior 
column ;  entering  below  the  eighth  thoracic  segment  they  flow 
through  the  fasciculus  gracilis,  or,  entering  above  the  eighth 
thoracic  segment,  they  ascend  through  the  fasciculus  cuneatus. 
In  either  case  they  arrive  in  one  of  the  nuclei  of  the  posterior  col- 
umn, namely,  the  nucleus  funiculi  gracilis  or  the  nucleus  funiculi 
cuneati.  Thence  the  impulses  may  proceed  either  by  a  direct 
or  by  an  indirect  route. 

1.  The  direct  route  carries  the  impulses  by  way  of  the  medial 
fillet  through  the  sensory  decussation  of  the  medulla,  the  forma- 
tio  reticularis  of  pons  and  mid-brain,  to  the  lateral  nucleus  of  the 
thalamus,  from  which  they  are  conducted  by  the  cortical  fillet 
to  the  somaesthetic  area  of  the  cerebral  cortex.  In  their  last 
stage  the  impulses  run  from  the  thalamus  through  the  internal 
capsule  and  corona  radiata  to  the  posterior  central  gyrus  in  the 
equatorial  zone  of  the  hemisphere. 

Above  the  nuclei  funiculi  gracilis  et  cuneati,  that  is  in  the 
medial  fillet,  the  impulses  of  the  muscle-sense  travel  through 
a  fasciculus  distinct  from  that  conducting  impulses  of  light  and 
deep  touch,  and  from  that  conducting  impulses  of  tactile  dis- 
crimination; though  all  three  fasciculi  are  contained  within  the 
medial  fillet. 

2.  Indirect  Route. — Impulses  traveling  this  route  do  not 
ordinarily  reach  the  threshold  of  consciousness  and  become  sen- 
sations; they  merely  excite  cerebellar  reflexes.  However,  if  the 
impulses  are  powerful,  they  may  overflow  the  synaptic  re- 
sistance of  the  reflex  centers  and  continue  to  the  cerebrum. 
Then  by  this  route  impulses  from  the  nucleus  funiculi  gracilis 
and  nucleus  funiculi  cuneati  run  to  the  cortex  of  the  vermis 
cerebelli  superior  through  the  external  arcuate  fibers;  then  on, 
through  the  brachium  conjunctivum,  to  the  red  nucleus  and 
thalamus.  They  traverse  the  restiform  body  of  the  same  side, 
by  way  of  the  posterior  external  arcuate  fibers;  or,  by  way  of 
the  anterior  external  arcuate  fibers,  they  traverse  the  fillet 
decussation  of  the  medulla  and  the  opposite  restiform  body  to 
reach  the  vermis  cerebelli  superior.     From  the  cerebellar  cortex, 


438 


TRACING    OF   IMPULSES 


rachium  conjunctivum 
Pons  and  cerebellum 


Tract  from  inferior  lateral 
nucleus  to  cerebellum  via  the 
restiform  body 


Angle  in  ventral  spino- 
cerebellar tract 


Medulla 


Gowers's )  Spino-thalamic  tract 
Tviri*     f  ventral  spino-cere- 
T'^^*    Jbellartract 


V  nerve 


IX  nerve 


X  nerve 


Spinal  nerves 


Fig.   152. — Common  sensory  paths,  pain,  temperature  and  touch,  by  way  of 
ventral  spino-cerebellar  and  spino-thalamic  tracts.     Diagrammatic.     (Original.) 

Posterior  root-fibers  connected  with  this  path  end  in  the  center 'of  the  crescent  and  in  the 
base  of  the  anterior  columna  of  both  sides;  and  the  ascending  fibers  rise  partly  on  the  same 
and  partly  on  the  opposite  side;  the  crossed  fibers  run  through  the  white  anterior  commissure . 


PAIN  AND   TEMPERATURES  PATHS  439 

the  impulses  continue  through  cortical  axones  to  the  nucleus 
dentatus,  whose  axones  conduct  them  to  the  red  nucleus  and 
thalamus  of  the  opposite  side.  The  greater  number,  therefore, 
cross  over  in  the  tegmentum  of  the  mid-brain.  Their  course 
from  the  red  nucleus  and  thalamus  is  through  the  cortical  fillet 
to  the  cortex. 

These  impulses  from  the  spinal  netves  go  to  the  upper  two- 
thirds  of  the  posterior  central  gyrus,  those  from  the  lower  extrem- 
ity to  the  upper  third  and  those  from  the  arms  to  the  middle 
third  (Spiller). 

Through  Cerebral  Nerves  and  Medial  Fillet  (Fig.  149). — 
As  crossed  fibers  from  the  terminal  nuclei  of  the  trigeminal,  the 
vestibular,  the  glossopharyngeal  and  the  vagus  nerves  join  the 
medial  fillet  and  run  to  the  thalamus,  so  muscular  and  tactile 
sensations  transmitted  by  those  cerebral  nerves  to  their  nuclei 
in  the  medulla  and  pons  are  carried  by  the  medial  fillet  to  the 
lateral  nucleus  of  the  thalamus  on  the  opposite  side.  The  corti- 
cal fillet  conducts  them  to  the  lower  portion  of  the  posterior 
central  gyrus  in  the  somaesthetic  area. 

n.  Paths  Conveying  Pain,  Temperature  and  Tactile  Im- 
pressions. Spinal  and  Cerebral.  Through  Spino-thalamic 
and  Ventral  Spino-cerebellar  Tract  (Fig.  150). — In  the  spinal 
cord,  medulla  and  pons  these  constitute  one  tract,  commonly 
called  Gowers^  tract.  They  separate  just  below  the  isthmus, 
whence  the  spino-thalamic  tract  continues  to  the  thalamus 
and  the  other  turns  back  to  the  cerebellum.  They  appear 
to  form  the  only  paths  for  pain  and  temperature  impulses. 
These  impulses  enter  the  gray  crescent  of  the  cord  on  both  sides 
through  the  posterior  nerve  roots.  A  large  number  decussate 
via  the  intrinsic  axones  in  the  gray  commissure;  the  rest  de- 
cussate in  the  first  stage  of  the  ascending  tracts,  crossing  in  the 
white  anterior  commissure,  and  run  upward  through  the  spino- 
thalamic and  ventral  spino-cerebellar  tracts  of  the  opposite 
side;  they  run  to  the  thalamus  and  to  the  cortex  of  the  superior 
worm  of  the  cerebellum.  In  the  cord  they  ascend  along  the 
lateral  surface.  They  run  dorsal  to  the  olive  in  the  lateral 
area  of  the  medulla  oblongata,  and  through  the  lateral  part  of 


440  TRACING    OF   IMPULSES 

the  formatio  reticularis  of  the  pons  to  the  angle  in  Gowers'  tract 
situated  near  the  isthmus.  From  the  angle,  just  below  the 
quadrigeminal  bodies,  the  cerebellar  impulses  run  backward 
with  the  tract  through  the  superior  medullary  velum  to  the 
cortex  of  the  vermis  cerebelli  superior;  the  remainder  run 
upward  to  the  thalamus,  and  from  that  to  the  posterior  central 
cortex.  Coordinating  reflex  impulses  are  excited  in  the  cere- 
bellum, which  reach  the  motor  nuclei  in  the  usual  ways :  through 
the  cortico-nuclear  neurones,  the  cerebello-tegmental  tracts,  and 
the  vestibulo-spinal,  rubro-spinal  and  thalamo-spinal  tracts. 
These  impulses  may  also  pass  to  the  conscious  centers  of  the  cere- 
brum. The  common  course  of  sensory  impulses  from  the  cere- 
bellar to  the  cerebral  cortex  is,  as  already  described,  through 
nucleus  dentatus  and  brachium  conjunctivum  to  opposite  red 
nucleus  and  thalamus.  Having  arrived  in  the  thalamus,  they 
proceed  thence  by  the  cortical  fillet  to  the  somaesthetic  cortex. 

Certain  fibers  of  Gowers'  tract  diverge  from  the  others,  in 
the  medulla  oblongata,  and  terminate  in  the  inferior  lateral 
nucleus.  Impulses  of  pain  and  temperature,  following  the  same 
course,  enter  the  lateral  nucleus,  and  are  carried  on  through  the 
restiform  body  to  the  cerebellum  by  the  tract  from  the  lateral 
nucleus  to  the  cerebellar  cortex,  thence  to  the  somaesthetic  area 
as  previously  given. 

Through  Cerebral  Nerves  and  the  Spino-thalamic  Tract 
(Fig.  150). — Pain  and  temperature  impulses  are  transmitted  by 
certain  fibers  of  the  vagus,  glossopharyngeal  and  trigeminal 
nerves  to  their  terminal  nuclei.  From  those  nuclei  they  are 
conducted  by  axones  which  probably  enter  into  the  spino- 
thalamic tract  and  perhaps  into  the  ventral  spino-cerebellar 
tract  to  the  thalamus  and  to  the  cerebellar  cortex.  The  path 
from  either  point  to  the  posterior  central  gyrus  is  now  familiar. 

The  Short  Fiber  Paths.- — What  special  varieties  of  common 
sensation  are  conducted  through  these  paths  is  unknown. 
Under  certain  conditions  perhaps  they  may  carry  all  varieties, 
(i)  The  antero-lateral  fasciculus  proprius  and  formatio  reticu- 
laris contain  ascending  axones  which  may  convey  sensory  im- 
pulses from  the  gray  matter  of  the  cord,  received  from  the  poste- 


OLFACTORY  PATH  44 1 

rior  roots  of  the  spinal  nerves,  and  from  terminal  nuclei  in  medulla 
and  pons  which  receive  the  common  sensory  fibers  of  cerebral 
nerves,  upward  to  the  thalamus  of  the  opposite  side.  The  course 
from  the  thalamus  is  by  way  of  the  cortical  fillet. 

Destruction  of  any  of  the  above  sensory  paths  causes  diminu- 
tion or  loss  of  the  especial  variety  of  impulse  which  travels  that 
path.  Destruction  of  the  posterior  white  columns  produces 
loss  of  muscular  sensations  and  gives  rise  to  ataxia.  Interrup- 
tion of  Gowers^s  tract  (spino-thalamic  and  ventral  spino-cere- 
bellar  tracts)  abolishes  pain  and  temperature  sensations  while 
touch  is  not  much  affected. 

2.  Special  Sensations 

Impulses  producing  the  sensations  of  smell,  sight,  hearing 
and  taste  are  carried  from  the  respective  organs  of  sense  to  the 
brain  by  the  following  nerves:  The  olfactory,  the  optic,  the 
auditory,  and  the  glossopharyngeal  and  intermediate  nerves. 

Olfactory  Path  (Figs.  151  and  21). — Impulses  of  smell  origi- 
nate in  the  upper  third  of  the  nasal  mucous  membrane.  They 
run  through  the  olfactory  nerves  to  the  second  layer  in  the  bulb, 
where  they  are  transferred  to  the  dendrites  of  the  mitral  and 
brush  cells.  By  the  axones  of  these  cells  they  are  carried  back- 
ward through  the  olfactory  tract  to  the  third  order  neurones 
whose  cell-bodies  are  located  in  the  cortex  of  the  tract,  the  olfac- 
tory triangle,  the  anterior  perforated  substance  and  the  septum 
pellucidum.  The  third  order  neurones  form  the  olfactory  strice; 
they  conduct  the  impulses  to  the  cortical  center,  the  hippocampal 
formation,  and  to  certain  reflex  centers,  the  thalamus,  the  amyg- 
dala, the  nucleus  habenulae,  etc.  The  lateral  stria  is  most  direct ; 
it  bears  the  olfactory  impulses  around  the  anterior  perforated 
substance  to  the  uncus  hippocampi.  The  medial  stria  (the 
stria  Lancisii)  reaches  the  cortical  center  by  encircling  the 
corpus  callosum;  it  conveys  the  impulses  by  way  of  the  gyrus 
subcallosus,  gyrus  supracallosus,  gyrus  subsplenialis  and  fas- 
ciola  cinerea,  and  fascia  dentata  to  the  hippocampus.  The 
intermediate  stria  comprises  four  bundles  of  fibers,  only  one  of 


442 


TRACING   OF   IMPULSES 


which  terminates  in  the  cortical  center  of  smell;  the  other  three 
etid  in  subcortical  centers  concerned  with  the  reflex  functions 
of  smell,  (i)  The  olfacto-hippocampal  bundle  carries  impulses 
from  the  olfactory  triangle,  perforated  substance  and  septum 
pellucidum  to  the  cortical  center  through  the  body  and  crus  of 
the  fornix.     (2)  The  olfacto-amygdalate  bundle  bears  impulses 


Central  ependymal 
cells 


Fibers  of  the  olfac- 
tory tract. 


Mitral  cells. 


Glomeruli* 


Olfactory  nerves. 


Olfactory  fibers  in 
the  nasal  mucous 
membrane. 


Olfactory  cells. 


Fig.  1 53 . — Chief  elements  of  the  olfactory  bulb.     (Gordinier  after  Van  Gehuchten.) 


from  similar  third  order  stations  up  to  the  thalamus  and,  then, 
forming  the  stria  terminalis,  takes  them  on  to  the  nucleus  amyg- 
dalae; some  of  these  cross  through  the  anterior  commissure. 
(3)  The  olfacto-habenular  bundle  conducts  olfactory  impulses 
from  perforated  substance  and  septum  pellucidum  to  both  nuclei 
habenulae  through  the  stria  meduUaris  thalami  and  the  com- 


VISUAL  PATH  443 

missura  habenularum;  also  to  quadrigeminal  colliculi.  (4)  The 
olfacto-mesencephalic  bundle  carries  impulses  from  the  cortex 
of  the  olfactory  tract  to  tuber  cinereum,  mammillary  body, 
tegmentum  of  mid-brain,  pons  and  medulla  and  through  fibers 
that  join  the  medial  longitudinal  bundle,  even  into  the  spinal 
cord.  In  the  brain-stem  and  spinal  cord,  these  olfactory  im- 
pulses probably  enter  motor  nuclei  and  excite  reflexes. 

Optic  Path  (Figs.  152  and  153). — Impulses  of  sight  originate 
in  the  rods  and  cones  of  the  retinae  and  traverse  three  or  more 
series  of  neurones  to  the  terminal  nuclei  of  the  optic  tracts; 
namely,  the  rod  and  cone,  the  bipolar,  and  the  ganglionar  neu- 


FiG.  154. — The  chief  retinal  elements.     (After  Bruhaker.) 
Cells,  s'  z'.  Visual  cells  with  their  peripheral  terminations,     s.  Rods.     z.  Cones,     b.  Bi- 
polar cells,     g.  Ganglion  cells  from  which  arise  the  axones  of  the  optic  nerve. 

rones.  The  axones  of  the  last  form  the  optic  nerves  and  the 
visual  part  of  the  optic  tracts.  From  the  right  halves  of  both 
retinae  and  from  the  left  halves  of  both,  impulses  run  through 
the  corresponding  tract  to  the  lateral  geniculate  body  and  the 
pulvinar  of  the  thalamus;  also  to  the  superior  quadrigeminal 
colliculus.  The  latter  produces  ocular  and  pupillary  reflexes. 
From  the  lateral  geniculate  body  and  pulvinar  the  thalamo- 
occipital  radiation  carries  the  impulses  through  the  pars  occipi- 
talis of  the  internal  capsule  to  the  half- visual  center  in  the  cu- 
neus,  gyrus  lingualis  and  the  pole  of  the  occipital  lobe.  Impulses 
from  the  nasal  halves  of  the  retinae  decussate  in  the  optic  chi- 


TRACING   OF   IMPULSES 


Fig.  155. — The  optic  path.     (Original.) 


AUDITORY  AND   EQUILIBRATORY  PATHS  445 

asma;  those  from  the  temporal  halves,  for  the  most  part  at  least 
remain  on  the  same  side,  but  a  few  may  cross  through  the  quad- 
rigeminal  colliculi  and  brachia  superiora.  Impulses  from  the 
nasal  half  and  from  the  temporal  half  of  the  macula  lutea  are 
conducted  equally  by  both  optic  tracts.  Hence  destruction  of 
one  tract  causes  hemianopsia,  preserving  the  vision  in  the  corre- 
sponding half  of  each  visual  field,  and  also  diminishes  the  acute- 
ness  of  macular  vision  in  both  eyes. 

Auditory  Paths. — There  are  two  auditory  paths,  cochlear 
and  the  vestibular.  The  former  is  concerned  with  hearing  and 
the  latter  with  equilibrium. 

1 .  The  Cochlear  Path  (Figs.  74,  93  and  119) . — Im^pulses  of  hear- 
ing originate  in  the  organ  of  Corti.  They  are  transmitted  by 
the  rods  and  hair  cells  of  Corti  to  the  dendrites  of  the  spiral  gan- 
glion. Traversing  the  dendrites  and  cell-bodies  of  that  ganglion 
they  enter  the  axones  which  form  the  cochlear  nerve  and  run 
backward  to  the  terminal  nucleus  of  that  nerve  in  the  medulla. 
Both  the  ventral  and  the  lateral  portions  of  the  cochlear  nucleus 
receive  the  impulses  of  hearing.  From  the  cochlear  nucleus  they 
run  either  lateral  and  dorsal  to  the  restiform  body  and  cross  to 
the  opposite  side  through  the  medullary  striae  and  trapezoid 
body,  or  they  run  medial  to  the  restiform  body  and  enter  at  once 
into  the  trapezoid  body.  By  either  course  they  reach  the  lateral 
fillet  and  chiefly  the  opposite  one.  The  lateral  fillets  conduct 
the  impulses  to  the  inferior  quadrigeminal  colliculi;  the  brachia 
inferiora  to  the  medial  geniculate  bodies,  and  the  thalamo- 
temporal  radiations  to  the  third  and  fourth  fifths  of  the  superior 
temporal  and  to  the  transverse  temporal  gyri  of  the  cerebrum. 
Through  the  lateral  fillet,  impulses  producing  reflex  reach  the 
quadrigeminal  colliculi  and  thence  by  the  anterior  tecto- 
spinal bundle  pass  to  motor  nuclei  and  also  through  the  oli- 
vary pedicle  and  medial  longitudinal  bundle  they  reach  the  nu- 
clei of  the  sixth,  fourth  and  third  cerebral  nerves. 

2.  Vestibular  Path. — The  extent  of  the  vestibular  conduction 
path  is  from  the  acustic  areas  of  the  utricle,  saccule  and  semi- 
circular canals  to  the  vestibular  nuclei  in  the  floor  of  the  fourth 
ventricle:  and  thence  to  the  cerebellum  and  to  the  cortical  area 


44^  TRACING   OF  IMPULSES 

of  equilibrium,  according  to  Mills,  in  the  temporal  cortex.  It  is 
the  path  of  space  sense.  Through  the  vestibular  nerve  the  im- 
pulses reach  the  dorso-medial,  the  dorso-lateral  and  superior 
nucleus,  and  the  nucleus  of  the  descending  root  in  the  floor  of 
the  fourth  ventricle. 

The  impulses  may  pursue,  from  the  terminal  nuclei  in  the 
ventricular  floor,  either  a  direct  or  an  indirect  course  to  the 
cerebral  cortex. 

1 .  By  the  direct  course  they  run  through  the  opposite  medial 
fillet  and  certain  fibers  in  the  cortical  fillet,  perhaps  the  ventral 
stalk  of  the  thalamus,  to  the  middle  and  inferior  temporal  gyri. 

2.  The  impulses  run  to  the  cerebellum,  by  the  indirect  course ^ 
through  the  fibers  of  the  vestibular  nerve  that  run  without 
interruption  to  nucleus  fastigii  and  the  nucleo-cerebellar  fibers 
which  run  from  each  of  the  vestibular  nuclei  to  the  cerebellar 
cortex.  Both  sets  of  fibers  pass  through  the  restiform  body,  but 
only  the  latter  reaches  the  cortex.  They  excite  in  the  cere- 
bellum impulses  of  equilibrium  and  then  continue  upward. 
From  the  cerebellum  the  course  of  the  impulses  is,  presumably, 
through  the  brachium  conjunctivum  to  the  red  nucleus  and  thala- 
mus of  both  sides  and  thence  to  the  cortex. 

Impulses  concerned  with  reflexes  run  from  the  vestibular 
nuclei  in  the  floor  of  the  fourth  ventricle,  (a)  to  the  opposite 
nuclei  of  motor  cerebral  nerves  via  the  medial  longitudinal  bun- 
dle; (b)  to  the  quadrigeminal  coUiculi  through  the  superior  fillet; 
(c)  to  the  motor  nuclei  of  spinal  nerves  through  the  vestibulo- 
spinal tract;  and  from  the  cerebellar  cortex  the  impulses  reach 
the  motor  nuclei  of  both  cranial  and  spinal  nerves,  as  follows: 
through  the  cortico-nuclear  neurones  to  the  cerebellar  nuclei; 
the  cerebello-tegmental  tracts  from  those  nuclei,  through  the 
brachium  conjunctivum  and  restiform  body,  to  the  brain-stem; 
and  then  complete  their  journey  through  the  vestibulo-spinal, 
rubro-spinal,  and  thalamo-spinal  tracts. 

The  Gustatory  Paths. — They  extend  from  the  tongue  to  the 
nucleus  tractus  solitarii  in  the  medulla  and  thence  probably 
through  the  opposite  formatio  reticularis  and  internal  capsule  to 
the  taste  area  in  the  gyrus  cinguli  (Flechsig).     There  are  two 


LESIONS  OF  SPECIAL  SENSE  PATHS  447 


paths  from  the  tongue  to  the  nucleus  of  the  solitary  tract. 
Those  impulses  from  the  base  of  the  tongue  and  the  palate  run 
through  the  ninth  nerve  and  those  from  the  anterior  two-thirds  of 
the  tongue  through  the  chorda  tympani  and  intermediate  nerve 
to  the  medulla  (A.  F.  Dixon,  Keen  and  Spiller,  H.  Gushing,  etc.). 
Possibly,  gustatory  impulses  originating  in  the  palate  may  tra- 
verse the  descending  palatine  nerves  and  the  great  superficial 
petrosal  nerve  to  reach  the  geniculate  ganglion  on  the  facial  and 
then  continue  through  the  intermediate  nerve  to  the  solitary 
tract.  All  impulses  arriving  at  this  nucleus  of  the  solitary 
tract  probably  complete  their  journey  in  two  stages:  Firsts 
through  the  formatio  reticularis  to  the  opposite  thalamus,  and 
second y  through  internal  capsule  to  the  cortex.  May  and  Horsley 
have  traced  the  gustatory  tract  from  the  nucleus  of  the  solitary 
tract  upward  through  the  reticular  formation  close  to  the  cen- 
tral gray  substance  and  dorso-lateral  to  the  medial  longitudinal 
bundle,  to  the  lateral  nucleus  of  the  thalamus;  the  tract  enters 
the  internal  medullary  lamina  of  the  thalamus  and  terminates 
in  the  medial  part  of  the  dorsal  third  of  the  great  lateral  nucleus 
(Brain,  Vol.  33) .  The  position  of  the  gustatory  radiation  in  the 
internal  capsule  is  not  yet  determined;  between  the  optic 
radiation  and  the  parietal  stalk  of  the  thalamus  is  the  most 
probable  location. 

Destruction  of  the  olfactory  conduction  path  on  one  side 
causes  anosmia  on  the  same  side;  of  the  optic  tract  or  radiation, 
atrophy  and  destruction  in  the  corresponding  halves  of  both 
retinae;  reflexes  are  abolished  in  the  affected  area  in  the  first 
case,  but  preserved  for  a  time  when  the  lesion  is  in  the  optic 
radiation;  interruption  of  the  auditory  path  above  the  pons, 
deafness  chiefly  on  the  opposite  side  and  interruption  of  the 
gustatory  path  above  the  medulla  oblongata  abolishes  taste  on 
the  same  side. 

m.  REFLEX  PATHS 

There  is  no  visible  limit  to  the  number  of  reflex  paths.  Hence 
no  attempt  will  be  made  to  give  them  completely,  but  a  few 
examples  of  various  kinds  will  be  given  which  may  assist  the 


448  TRACING   OF   IMPULSES 

student  to  trace  others  and  be  suggestive  of  their  great  multi- 
plicity and  importance.  Under  certain  conditions,  unquestion- 
ably, the  sensory  and  motor  paths  that  have  been  traced  are  but 
the  afferent  and  efferent  limbs  of  reflex  arcs. 

Reflex  arcs  are  formed  (i)  by  the  sensory  and  motor  fibers 
of  spinal  nerves  associated  in  the  gray  matter  of  the  cord;  (2) 
by  the  sensory  and  motor  fibers  of  cerebral  nerves  which  are 
connected  in  the  brain;  (3)  by  afferent  spinal  fibers  connected 
by  the  ascending  fibers  of  the  fasciculi  proprii,  with  efferent  cere- 
bral fibers;  (4)  by  afferent  cerebral  and  efferent  spinal  nerve  fi- 
bers, the  two  being  associated  by  the  anterior  and  lateral  tecto- 
spinal bundles,  the  reticulo-spinal  tracts,  the  fasciculi  proprii, 
the  spinal  tract  of  the  fifth  nerve,  the  vestibulo-spinal  tract, 
etc. ;  and  (5)  coordinated  cerebellar  reflexes  through  spinal  and 
cerebral  nerves. 

I.  Spinal  Reflexes  (Figs.  72,  154  and  155). — In  the  simplest 
spinal  reflexes,  the  afferent  fibers  of  the  arc  arborize  about  the 
cell-bodies  whose  axones  constitute  the  efferent  fibers;  the 
afferent  and  efferent  fibers  are  connected  by  one  or  more  sets 
of  intervening  neurones  in  the  next  grade  of  reflex  arc.  The 
intercalated  neurones  connect  the  posterior  columna  of  gray 
matter  with  both  anterior  columnae,  in  the  same  segment;  and, 
by  means  of  T-branched  axones  in  the  fasciculi  proprii,  they 
connect  a  single  segment  of  the  posterior  columna  with  many 
segments  of  the  anterior  columnae,  above  and  below  the  seg- 
ment receiving  the  afferent  limb  of  the  reflex  arc.  Among  these 
are  the  skin  and  muscle  reflexes,  such  as  the  plantar,  the  patellar, 
the  gluteal  and  the  cremaster  reflexes,  the  involuntary  with- 
drawing of  a  part  from  a  source  of  irritation,  etc. 

More  complicated  spinal  reflexes  are  those  of  defecation,  mic- 
turition, parturition,  vasomotor  reflexes,  cardio-accelerator 
reflexes,  etc.  The  impulses  traverse  at  least  three  neurones  in 
these  reflexes;  because  all  efferent  white  rami  communicantes 
terminate  in  some  ganglion  proximal  to  the  organ  supplied.  As 
an  example,  trace  a  defecation  reflex. 

Defecation  Reflex. — The  rectum  is  supplied  by  the  third  and 
fourth  sacral  nerves  and  bv  branches  of  the  inferior  mesenteric 


REFLEXES 


449 


and  hypogastric  plexuses.  Irritation  of  the  sensory  endings  in 
the  mucous  membrane  is  caused,  normally,  by  the  presence  of 
feces.  The  impulses  caused  thereby  run  to  the  special  defeca- 
tion center  in  the  lumbar  enlargement  of  the  spinal  cord,  either 
by  way  of  the  sacral  nerves  or  through  the  sympathetic  plexuses, 
the  ganglionated  cord,  and  the  rami  communicantes  to  the  lum- 
bar nerves,  through  the  posterior  roots  of  which  they  reach  the 
center  in  the  cord.  From  the  defecation  center  the  impulses 
pursue  two  courses:  (a)  They  descend  through  the  third  and 
fourth  sacral  nerves  and  cause  inhibition  in  the  circular  fibers  of 
the  rectum  and  contraction  of  the  longitudinal  muscle,  (b) 
This  action  is  immediately  followed  by  impulses  which  pursue 
the^sympathetic  course,  through  the  anterior  roots  of  the  lumbar 


Fig.  156. — Diagram  of  a  simple  reflex  arc.     (After  Brubaker.) 

I.  Sentient  surface.     2.  Afferent  nerve.     3.  Emissive  or  motor  cell.     4.  Efferent  nerve. 

5.   Muscle. 

nerves,  the  rami  communicantes,  the  ganglionated  cord,  and  the 
inferior  mesenteric  and  hypogastric  plexuses,  to  the  rectum. 
They  cause,  in  succession  from  above  downward,  contraction  of 
the  circular  muscle  of  the  rectum.  The  two  series  of  impulses 
thus  open  a  way  for  the  passage  of  fecal  matter  and  then  force 
it  through  the  opening  unless  prevented  by  the  voluntary  con- 
traction of  the  external  sphincter. 

2.  Cerebral  Reflexes. — The  simplest  of  these  reflexes  are 
such  as  spasm  of  the  muscles  of  mastication  caused  by  a  bad 
toothy  in  which  both  limbs  of  the  arc  are  formed  by  the  tri- 
geminal nerve.  Again,  the  facial  expression  of  pain  due  to  the 
same  cause.  In  this  the  impulses  traverse  the  trigeminal  nerve 
and  by  the  collaterals  of  its  root-fibers  reach  the  nucleus  of  the 
29 


450 


TRACING   OF  IMPULSES 


facial.  Through  the  facial  they  cause  contraction  of  certain 
muscles  of  expression.  Facial  spasm  in  tic  douloureux  is  due 
to  the  same  reflex.  The  involuntary  expansion  of  the  nostrils 
upon  the  detection  of  a  faint  odor  is  due  to  an  olfactory-facial 
reflex.  The  connection  of  the  terminal  nucleus  and  cortical 
center  of  the  olfactory  nerve  with  the  genetic  nucleus  of  the 
facial  nerve  is  very  much  involved;  it  may  be  estabhshed  as 
follows  with  facial  and  other  motor  nuclei:  (i)  by  ]the  hippo- 


FiG.  157. — A  more  complicated  spinal  reflex  arc,  involving  the  fasciculi  proprii. 

{Brubaker  after  Kolliker.) 

Diagram  showing  the  relation  of  the  third  neurone  a,  to  the  afferentj  neurone  b,  and  to  the 

efferent  neurones  c,  c,  c. 


campo-mammillary  fasciculus  of  the  fornix,  the  mammillo- 
thalamic  bundle  and  the  thalamo-spinal  tract;  (2)  the  olfacto- 
amygdalate  fasciculus,  forming  stria  terminalis,  the  strio-fugal 
tracts  and  their  continuations  down  the  brain-stem  and  cord; 
(3)  the  hippocampo-mammillary  fasciculus  of  the  fornix,  the 
mammillo-tegmental  bundle  and  the  mammillary  peduncle, 
which  also  runs  to  the  tegmentum,  and  the  dorsal  longitudinal 
bundle  of  Schiitz;  (4)  the  hippocampo-habenular  fasciculus  of 
the  fornix  and  the  olfacto-habenular  bundle,  the  two  forming 


REFLEX  ARCS 


451 


Stria  meduUaris  thalami,  the  habenulo-peduncular  fasciculus 
(fasciculus  retrofiexus),  and  the  interpedunculo-tegmental  bun- 
dle; and  (5)  the  olfacto-mesencephalic  fasciculus  (basal  bundle 
of  Wallenberg),  which  runs  from  the  cortex  of  the  olfactory 
tract  to  tuber  cinereum,  mammillary  body,  tegmentum  of  mid- 
brain, pons  and  medulla,  and  even  into  spinal  cord.  The  last 
tract  in  each  of  the  above  five  groups  terminates  in  connection 
with  the  motor  nuclei  of  cranial  and  spinal  nerves.     Squinting, 


Fasciculus  cuneatus 


*    Cephalic  branch  of  spinal  ganglion  neurone 


-••••  Dorsal  (posterior)  root 


Fig.  158. — Reflex  arc  with  both  somatic  and  visceral  efferent  limbs. 


due  to  bright  light,  is  produced  by  an  arc  composed  of  the 
visual  path,  the  corticifugal  part  of  the  occipi to- thalamic 
radiation,  the  anterior  tecto-spinal  bundle  and  the  facial  nerve. 
Substitute  the  oculomotor  nerve  for  the  facial  and  add  neurones 
of  ciliary  ganglion  and  we  have  the  arc  for  pupillary  contraction 
under  the  same  conditions. 

Salivary  reflexes,  in  which  the  sight  of  a  fine  dinner  or  the 
smell  of  it  causes  the  flow  of  saliva;  coughing,  sneezing,  vomiting 
reflexes  and  deglutition  reflexes  are  complicated,  but,  knowing 


452  TRACING    OF   IMPULSES 

the  nerve  supply  of  the  parts  involved,  the  student  should  try 
to  trace  the  impulses. 

3.  Spino-cerebral  Reflexes. — Impulses  received  by  the  spinal 
cord  through  the  afferent  fibers  of  its  nerves  are  transmitted  by 
the  medial  longitudinal  bundle,  the  fasciculi  proprii  and  forma- 
tio  reticularis  to  the  nuclei  of  motor  cerebral  nerves.  Thus  is 
brought  about  the  movement  of  the  head  and  eyes  toward  the 
source  of  impulse,  a  change  of  facial  expression  to  agree  with 
the  painful  or  pleasing  character  of  the  impulses,  etc. 

Some  long  spino-cerebral  reflex  arcs  are  formed  by  the  af- 
ferent neurones  which  terminate  in  the  quadrigeminal  bodies, 
red  nucleus,  thalamus  and  lentiform  nucleus,  and  the  efferent 
neurones  whose  cell-bodies  are  located  in  those  nuclei.  The 
arc  of  the  red  nucleus  will  be  considered  with  the  cerebellar 
reflexes,  as  its  afferent  limb  passes  through  the  cerebellum. 
The  rejiex  arc  of  the  quadrigeminal  bodies  (tectum)  is  formed  by 
afferent  nerves  and  the  spino-tectal  fibers  of  Gowers's  tract  on 
the  afferent  side,  and  the  anterior  and  lateral  tecto-spinal  tracts 
and  motor  nerves  on  the  efferent  side.  The  arc  of  the  thalamus 
is  formed  in  part  by  the  spino-thalamic  tract  and  the  thalamo- 
spinal  tract,  completed  by  the  sensory  and  motor  nerves.  The 
thalamus  also  lies  in  the  lenticulo-spinal  path  and  in  the  cere- 
bellar reflex  arcs.  The  lentiform  nucleus  receives  impulses 
through  the  spino-lentiform  fibers  of  Gowers's  tract,  through  the 
thalamo-striate  and  hypothalamo-striate  fibers;  it  originates 
impulses  that  descend  to  motor  nuclei  by  way  of  the  thalamus, 
red  nucleus,  hypothalamic  nucleus  and  substantia  nigra,  as  its 
own  neurones  do  not  reach  motor  nerve  nuclei.  The  thalamo- 
spinal  and  rubro-spinal  tracts  establish  its  chief  connection 
with  the  spinal  cord.  According  to  Kinnier  Wilson,  the  len- 
ticulo-spinal impulses  steady  the  activity  of  the  lower  motor 
neurones;  they  prevent  hyper  tonicity,  rigidity  and  tremor. 

4.  Cerebro-spinal  Reflexes. — Of  these  there  are  many.  Let 
us  notice  three. 

Respiratory  Reflex. — Any  obstruction  or  irritation  in  the 
larynx  or  trachea  sends  an  impulse  through  the  vagus  nerve  to 
its  sensory  nucleus  and,  through  its  T-branched  axones  to  the 


EQUILIBRIUM  453 

nucleus  ambiguus,  nucleus  of  the  phrenic  nerve  and  nuclei  con- 
trolling the  accessory  muscles  of  respiration.  The  connection  of 
the  sensory  nucleus  of  the  vagus  with  these  motor  nuclei  is 
probably  established  through  the  medial  longitudinal  bundle 
and  the  fasciculi  proprii.  The  afferent  impulses  from  the 
larynx  first  inhibit  the  inspiratory  act  and  close  the  larynx  by 
contraction  of  all  the  constrictors;  then  there  follows  a  sudden 
and  powerful  expiratory  effort  which  drives  a  column  of  air 
through  the  partially  opened  glottis,  expelling  the  foreign  body 
and  producing  a  cough.  The  reflex  producing  a  sneeze  is  simi- 
lar; but  the  afferent  limb  of  its  arc  is  formed  by  the  trigeminal 
nerve,  the  fibers  supplying  the  nasal  mucous  membrane.  A 
powerful  reflex  inspiration  always  precedes  the  sneeze,  and  the 
soft  palate  is  brought  down  against  the  tongue  so  that  the  col- 
umn of  air  is  forced  through  the  nose. 

Equilibrium  Reflex  (vestibulo-spinal  reflex). — The  simplest 
arc  of  equilibrium  between  the  eighth  cerebral  nerve  and  the 
spinal  nerves  is  formed  by  the  neurones  of  the  vestibular  ganglia 
(Scarpa's),  the  vestibulo-spinal  tract  and  the  motor  neurones  of 
the  anterior  columna  of  the  spinal  cord.  A  more  complicated 
arc  includes  the  fibers  of  the  vestibular  nerve  that  run  through 
restiform  body  to  the  nucleus  fastigii,  and  the  nucleo-cerebellar 
fibers  which  run  from  the  vestibular  nuclei  through  the  same 
body  to  the  cerebellar  cortex.  Both  these  fasciculi  belong  to 
the  afferent  limb  of  the  reflex  arc.  The  cortico-nuclear  axones  of 
Purkinje's  neurones  iormthe  fl^rst  link  in  the  efferent  limb.  The 
cerebello-tegmental  tracts  form  the  second  link,  connecting  the 
cerebellar  nuclei  with  the  nuclei  of  the  brain-stem;  they  run 
through  the  brachium  conjunctivum  to  red  nucleus,  thalamus, 
and  the  motor  nuclei  of  the  mid-brain,  pons  and  medulla,  and 
through  the  restiform  body  to  the  nucleus  of  Deiters  and  motor 
nuclei  in  the  medulla .  The  third  link  of  the  efferent  limb  extends 
from  the  terminations  of  the  cerebello-tegmental  tracts  to  the 
nuclei  of  motor  nerves,  and  more  especially  the  spinal  nerves. 
This  third  link  is  a  threefold  one,  composed  of  the  thalamo- 
spinal,  rubro-spinal  and  vestibulo-spinal  tracts.  The  motor 
nerves  complete  the  efferent  Hmb  of  the  vestibular  arc  of  equi- 


454  TRACING   OF  IMPULSES 

librium.  By  this  arc  it  is  possible  for  the  movements  of  labyrin- 
thine fluid  to  preserve  equilibrium. 

Pupillary  Reflexes. — Pupillary  dilatation  belongs  to  the  cere- 
brospinal group  of  reflexes.  The  cilio-spinal  center  is  in  the 
cervical  enlargement  of  the  spinal  cord.  It  receives  optic  im- 
pulses through  both  the  tecto-spinal  bundles  from  the  corpora 
quadrigemina.  The  superior  quadrigeminal  colliculi  receive 
those  impulses  by  two  routes :  First,  directly  through  the  fibers 
of  the  lateral  root  of  the  optic  tract  and  second,  indirectly 
through  corticifugal  fibers  in  the  occipito-thalamic  radiation, 
and  the  brachium  superius.  By  the  latter  route  the  optic 
impulses  which  have  reached  the  visual  area  of  the  occipital 
lobe  by  way  of  the  intrinsic  retinal  neurones  and  the  optic 
nerves,  tracts  and  radiation,  are  returned  to  the  lateral  genicu- 
late and  superior  quadrigeminal  bodies.  Thence  reaching  the 
cilio-spinal  center  through  both  the  tecto-spinal  bundles,  the 
impulses  take  the  following  course :  They  leave  the  spinal  cord 
through  the  anterior  roots  of  the  upper  thoracic  nerves  and  run 
in  succession  through  the  rami  communicantes,  the  cervical 
cord  of  the  sympathetic,  the  cavernous  plexus,  and  the  short  cil- 
iary nerves  to  the  radiating  fibers  of  the  iris,  causing  dilatation 
of  the  pupil. 

For  pupillary  constriction,  the  impulses  run  directly  from  the 
superior  quadrigeminal  colliculus  to  the  oculomotor  nucleus, 
traversing  the  anterior  tecto-spinal  bundle  only  through  the 
dorsal  tegmental  decussation  (Meynerti).  Then  through  the 
visceral  fibers  of  the  third  and  the  axones  of  the  ciliary  ganglion, 
which  form  the  short  ciliary  nerves,  they  reach  the  sphincter 
pupillae  muscle. 

Accommodation  for  near,  and  distant  vision  is  secured  through 
the  arcs  just  given.  Through  the  arc  of  pupillary  contraction, 
impulses  reach  the  circular  fibers  of  the  ciliary  muscle  and,  by 
their  contraction,  accommodate  for  near  vision.  The  meridional 
fibers  of  the  ciliary  muscle  being  supplied  by  the  cervical  sym- 
pathetic are  controlled  by  the  arc  of  pupillary  dilatation. 
Impulses  through  this  arc  cause  flattening  of  the  lens  and 
shortening  of  the  polar  axis  of  the  eye  so  that  the  focus  of  an 


CEREBELLAR   REFLEXES 

object  at  a  great  distance  falls  on  the  retina  and  the  eye  is 
thus  accommodated  for  distant  vision. 

5.  Cerebellar  Reflexes. — The  cerebellar  reflexes  connected 
with  the  vestibular  nerve  have  been  given  under  the  head  of 
equilibrium  reflexes.  Every  motor  nucleus  receives  impulses 
from  the  cerebellum.  The  impulses  excited  in  the  cerebellar 
cortex,  besides  toning  up  the  muscles  and  augmenting  the  power 
of  steady,  tonic  contraction,  coordinate  the  muscles  producing 
instinctive  movements  (running,  flying,  swimming,  etc.)  and  the 
muscles  performing  acquired  and  educated  movements;  and, 
furthermore,  control  many  of  the  motor  and  secretory  func- 
tions (sympathetic  functions)  of  the  great  viscera.  In  lower 
animals  all  these  reflexes  may  be  produced  without  the  inter- 
vention of  the  cerebellum. 

Through  Ventral  Spino-cerebellar  Tract. — Impulses  of  pain, 
heat  and  cold  received  by  the  gray  crescent  of  the  cord  through 
the  spinal  ganglion  neurones,  decussate  through  the  gray  and 
white  commissures  of  the  cord  and  ascend  Gowers's  tract  to  the 
brain,  running  through  the  spino-thalamic  and  spino-tectal 
tracts  to  thalamus  and  tectum  and  through  ventral  spino- 
cerebellar tract  to  cerebellar  cortex.  Those  carried  by  the  ven- 
tral spino-cerebellar  tract  ascend  the  lateral  surface  of  the  cord 
and  medulla,  dorsal  to  the  anterior  root-line  of  the  cord  and 
anterior  lateral  sulcus  of  the  medulla,  and  continue  through  the 
lateral  part  of  the  reticular  formation  of  the  pons  to  a  point 
above  the  root  of  the  trigeminal  nerve;  there,  the  tract  flexes 
backward  about  90  degrees,  winds  over  the  lateral  and  dorsal 
surface  of  the  brachium  conjunctivum  into  the  velum  medullare 
superius  of  the  cerebellum,  where  some  of  its  fibers  decussate; 
it  then  proceeds  through  the  corpus  medullare  cerebelli  to  the 
cortex  of  the  superior  vermis.  As  some  fibers  of  Gowers^s  tract 
end  in  the  inferior  lateral  nucleus  of  the  medulla,  some  pain  and 
temperature  impulses  may  reach  the  cerebellum  also  through 
the  restiform  body  traversing  the  reticulo-cerebellar  fibers  from 
the  lateral  nucleus.  Having  arrived  in  the  cortex  of  the  cere- 
bellum, the  pain  and  temperature  impulses  probably  assist  in 
the  production  of  the  impulse-complexes  characteristic  of  the 


456  TRACING    OF   IMPULSES 

cerebellum;  but  it  may  be  inferred  that  they  are  chiefly  con- 
cerned with  the  coordinations  adapted  to  an  escape  from  the 
offending  object.  Such  cerebellar  impulses  are  conducted  from 
the  cortex  to  the  cerebellar  nuclei  by  the  cortico-nuclear  fibers 
(axones  of  Purkinje^s  cells).  Whether  they  proceed  from  the 
cerebellar  nuclei  through  the  restiform  body  to  Deiters's  nucleus, 
or  through  the  brachium  conjunctivum  to  red  nucleus  and  thala- 
mus, it  has  not  yet  been  determined;  but  the  brachium  con- 
junctivum is  the  more  probable  course.  Rubro-spinal  and 
th  alamo-spinal  tracts  complete  the  conduction  to  the  motor 
nuclei  of  the  spinal  nerves,  and  the  spinal  nerves  produce  the 
reflex  contractions  necessary  to  escape  from  the  hot,  cold  or 
painful  stimulus.  Impulses  traveling  through  the  ventral 
spino-cerebellar  tract  may  also  reach  the  center  of  conscious- 
ness for  pain  and  temperature  in  the  thalamus  and  be  trans- 
formed into  sensations. 

Swimming. — The  reflex  mechanism  of  swimming  has  been 
studied  in  lower  forms  by  Coghill,  Herrick,  van  Gehuchten  and 
others.  In  amblystoma  tigrinum  the  mechanism,  according  to 
Coghill,  consists  (i)  of  a  series  of  afferent  neurones  whose 
dendrites  supply  skin  and  myotomes  (muscles)  and  whose  ax- 
ones ascend  the  spinal  cord  to  the  medulla,  forming  a  common 
afferent  path;  (2)  of  a  group  of  commissural  neurones  in  the 
medulla  which  connect  the  afferent  path  with  the  efferent  path; 
and  (3)  a  chain  of  efferent  neurones,  forming  a  common  motor 
path,  which  supplies  all  the  myotomes  of  that  side  with  motor 
fibers.  Of  course  this  mechanism  is  duplicated ;  an  afferent 
and  an  efferent  path  are  present  on  both  sides,  and  each  afferent 
is  connected  with  the  opposite  efferent  path  by  the  commissure 
in  the  medulla.  This  mechanism  may  be  set  into  operation  by 
any  external  stimulus.  If  an  extero-ceptive  stimulus  is  applied 
to  the  right  side  of  the  body,  the  impulse  traverses  some  per- 
ipheral nerve  to  the  cord  and  ascends  the  cord  to  the  medulla; 
there  it  passes  through  the  commissure  to  the  opposite  side  and 
excites  a  motor  impulse  in  the  efferent  neurones,  which  descends 
the  common  motor  path  of  the  left  side.  As  the  motor  impulse 
proceeds  down  that  side  it  causes  contraction  of  the  myotomes 


SWIMMING  AND   POSTURE   REFLEXES  457 

in  succession,  the  contraction  wave  advancing  gradually  toward 
the  tail.  The  result  is  a  bending  of  the  head,  and  later  of  the 
tail,  toward  the  left  side,  away  from  the  point  of  stimulation. 
The  contraction  of  the  myotomes  constitutes  the  second  stimu- 
lus; it  excites  proprio-ceptive  impulses  (muscle-sense  impulses) 
which,  first,  inhibit  the  contraction  of  the  myotome  in  which 
they  originated  and,  second,  ascend  the  afferent  path  to  the 
medulla,  cross  over  to  the  opposite  efferent  path  and  excite 
impulses  that  cause  contraction  of  the  right  myotomes  in  suc- 
cession from  head  to  tail.  While  left  flexion  is  still  present  in 
the  tail,  the  head  is  flexed  to  the  right;  the  first  S -flexure  is  the 
result.  The  contraction  of  the  right  myotomes  also  glides  tail- 
ward  and  produces  proprio-ceptive  impulses  which  inhibit  their 
own  contractions  and,  passing  through  the  afferent,  commissural 
and  opposite  efferent  path,  cause  contraction  of  the  left  myotomes 
in  regular  order  from  before  backward.  The  head  is  thus  bent 
to  the  left  while  the  tail  is  still  bent  toward  the  right;  the 
reversed  S-flexure  is  the  result.  The  alternating  production  of 
the  S-flexures  constitutes  the  swimming  movement. 

Posture  Reflex. — Posture  both  in  standing  and  walking  is 
maintained  by  a  reflex  mechanism  whose  stimuli  originate 
within  the  anti-gravity,  extensor  muscles.  This  synergic  group 
of  muscles  is  kept  in  a  state  of  gentle  tonic  contraction,  or  reflex 
tonus,  by  the  proprio-ceptive  impulses  induced  in  the  neuro- 
muscular and  neuro-tendinous  spindles  of  the  muscles  by  their 
own  contraction.  Those  proprio-ceptive  impulses  (muscle- 
sense  impulses)  ascend  the  afferent  nerves  and  the  posterior 
column  of  the  spinal  cord  to  the  nuclei  gracilis  and  cuneatus  of 
the  medulla;  thence  they  continue  to  the  cerebellar  cortex 
through  the  arcuate  fibers  in  the  restiform  body.  In  the  cere- 
bellar cortex,  they  excite  impulses  that  secure  a  gentle,  steady 
contraction  of  the  anti-gravity  muscles.  The  path  traveled 
from  the  cerebellar  cortex  to  those  muscles  probably  runs 
through  the  brachium  conjunctivum  to  red  nucleus  and  thala- 
mus; then  descends  the  rubro-spinal  and  thalamo-spinal  tracts 
to  the  gray  substance  of  the  cord,  whence  the  motor  fibers  of 


458  TRACING   OF  IMPULSES 

the  spinal  nerves  carry  the  impulses  to  the  muscles  which  pre- 
serve the  erect  posture. 

A  decapitated  dog  or  cat  cannot  stand;  the  end-brain  may- 
be removed  and  the  erect  posture  be  maintained;  but,  if  the 
section  be  made  through  the  thalamus  or  below  it,  the  animal 
is  unable  to  stand.  Hence,  the  coordinating  impulses  from  the 
cerebellar  cortex  probably  reach  the  spinal  cord  by  way  of  the 
red  nucleus  or  thalamus.  It  is  evident  that  walking  is  possible 
only  when  the  posture  mechanism  and  the  mechanism  of  stepping 
are  both  in  operation. 

Stepping  Reflexes. — The  reflex  step  has  been  studied  by 
Goltz,  Loeb,  Sherrington,  and  others.  In  the  dog  and  cat  the 
mechanism  of  the  step  for  the  hind  limbs  most  closely  resembles 
the  stepping  mechanism  of  man.  In  the  decapitated  dog  this 
is  as  follows:  (i)  The  ajfferent  spinal  neurones  which  supply  the 
muscles,  skin,  etc.,  of  the  hind  limbs.  (2)  Two  systems  of 
efferent  neurones  on  each  side,  one  supplying  the  flexors  and  the 
other  the  extensors  of  the  limb,  so  adjusted  or  attuned  that 
stimulation  of  one  system  inhibits  the  action  of  the  other  on 
the  same  side;  and,  furthermore,  these  efferent  systems  are  so 
adjusted  in  opposite  sides  of  the  cord  that  stimulation  of  the 
flexor  neurones  of  one  limb  equally  activates  the  extensor 
neurones  of  the  opposite  limb.  (3)  The  reflex  arcs  are  com- 
pleted by  intrinsic  neurones  of  the  cord,  associative  and  com- 
missural, which  join  the  afferent  and  efferent  limbs  together. 

This  mechanism  may  be  set  into  operation  by  flexing  or  ex- 
tending one  of  the  limbs,  by  applying  the  faradic  current,  by 
pinching,  etc.  Suppose  the  right  hind  limb  is  pinched.  An 
afferent  impulse  ascends  to  the  cord;  it  is  transferred  to  the 
efferent  neurones  of  both  sides  of  the  cord;  and  it  excites  the 
flexor  system  of  the  same  side  and  the  extensor  system  of  the 
opposite  side.  The  result  is,  first,  withdrawal  of  the  right  hind 
limb  from  the  offending  object  and,  second,  extension  of  the  left 
limb  in  an  effort  to  run  away.  The  stepping  motion  is  then  con- 
tinued by  proprio-ceptive  impulses  (muscle-sense  impulses) 
excited  in  the  neuro-muscular  and  neuro-tendinous  spindles  by 
the  tension  of  the  contracting  muscles.     The  contraction  of  the 


VISCERAL  REFLEX  ARCS  459 

flexors  in  the  right  limb  is  inhibited  by  a  cumulative  extensor 
impulse,  excited  by  the  tension  of  the  flexors,  which  becomes 
effective  when  contraction  is  complete;  this  impulse  excites  the 
extensor  neurones  of  the  same  side  and,  passing  through  the 
commissure  of  the  cord,  stimulates  the  flexor  neurones  of  the  left 
limb.  The  proprio-ceptive  stimuli  excited  in  the  contracting 
muscles  will  continue  the  alternate  flexion  of  one  limb  and  the 
extension  of  the  other  until  the  stepping  is  arrested  by  fatigue 
or  otherwise. 

Educated  Movements  of  the  Hands. — When  acquired  move- 
ments by  long  practice  become  automatic,  they  are  evidently 
performed  by  a  combined  mechanism  of  posture  and  movement 
similar  to  that  of  walking.  The  spinal  mechanism  secures  the 
reciprocal  stimulation  and  inhibition  of  antagonistic  systems 
of  neurones,  the  flexors  and  extensors;  and  the  cerebellar  mech- 
anism, as  described  under  posture  reflexes,  so  coordinates  the 
spinal  mechanism  as  to  obtain  the  proper  successive  postures  of 
hands  and  digits. 

Visceral  Paths  to  the  Cerebellum,  Spinal  and  Cranial. — 
Sympathetic  impulses  from  viscera  enter  the  dorsal  nucleus  (of 
Clark)  in  the  cord  and  the  dorsal  nucleus  of  the  vagus  in  the 
medulla.  Note  first  the  spinal  path.  Visceral  impulses  tra- 
verse the  white  rami  communicantes  and  the  posterior  roots  of 
the  spinal  nerves  to  the  dorsal  nucleus  of  Clark ;  they  ascend  to 
the  cerebellar  cortex  through  the  dorsal  spino-cerebellar  tract, 
which  runs  along  the  surface  of  the  cord  just  dorsal  to  the  mid- 
lateral  line,  and  continues  through  the  restiform  body  to  the 
cortex  of  the  vermis  superior  on  both  sides  of  the  median  plane. 
In  the  cerebellum  impulses  are  excited  that  maintain  muscle- 
tone  and,  probably,  coordinate  viscero-motor,  viscero-inhibitory, 
cardiac  accelerator,  secretory,  trophic,  and  other  sympathetic 
functions.  By  which  of  the  familiar  cerebello-fugal  paths  these 
impulses  descend  to  the  intermedio-lateral  nucleus  of  the  cord 
it  has  not  been  determined,  but  they  pass  down  through  the 
lateral  funiculus  of  the  cord.  Having  reached  the  intermedio- 
lateral  nucleus  (the  visceral  efferent  nucleus),  the  impulses 
continue  through  the  axones  of  that  nucleus  to  sympathetic 


460  TRACING   OF  IMPULSES 

ganglia,  whose  axones  complete  the  path;  the  axones  of  the 
intermedio-lateral  nucleus  constitute  the  small  fibers  in  the 
anterior  roots  of  the  spinal  nerves  and  the  efferent  fibers  of  the 
white  rami  communicantes;  axones  from  the  sympathetic  gan- 
glia, the  post-ganglionic  fibers,  convey  the  impulses  to  their 
destination,  the  gland  cells  and  smooth  and  heart  muscles. 

The  cranial  path  for  visceral  impulses  is  contained  chiefly  in 
the  vagus  nerve.  Sympathetic  impulses  ascend  the  afferent 
fibers  of  the  vagus  to  the  terminal  part  of  its  dorsal  nucleus 
(nucleus  of  ala  cinerea) ;  they  first  excite  reflex  impulses  in  the 
efferent  part  of  the  dorsal  nucleus  and,  then,  proceed  through 
axones  of  that  nucleus  (nucleo-cerebellar  fibers)  to  the  cere- 
bellar cortex,  by  way  of  the  restiform  body.  Cerebellar  im- 
pulses coordinating  cardiac  inhibition,  secretion,  etc.,  etc.,  in 
the  field  of  the  vagus,  are  returned  to  the  efferent  part  of  the 
dorsal  nucleus  through  the  cortico-nuclear  and  cerebello-teg- 
mental  fibers.  Then  the  vagus  carries  the  impulses  to  various 
sympathetic  ganglia,  whose  post-ganglionic  fibers  bear  them  on 
to  the  gland  cells  and  involuntary  muscles  innervated  through 
the  vagus. 


INDEX 


Abducent  nerve,  42,  364 

Accessory  lemniscus,  or  fillet,  243 
nerve,  44,  326,  354 
nucleus  funiculi  cuneati,  353 
processes  of  neurones,  422 

Acervulus  cerebri,  132 

Acustic  centers,  191 
nerve,  42,  362,  363 
radiation,  loi,  229,  247,  250 

Afferent  or  sensory  paths,  436 

Ala  cinerea,  323,  360 

Alveus,  21 

Anastomosing   canals    of   neurones, 
171 

Anastomotic  veins,  23 

Angular  gyrus,  65 

Ansa  lenticularis,  100,  226 
peduncularis,  100 

Anterior  central  gyrus,  61 

cerebellar  commissure,  290 
cerebral  artery,  16 
chorioidal  artery,  18 
column  of  medulla,  326,  327 
columna  of  gray  substance,  340, 

388,  389 
commissure,  133,  252 
horn  of  lateral  ventricle,  123 
inferior  cerebellar  artery,  27 
intermediate  sulcus,  387 
lateral  sulcus  of  medulla,  39,  318 
longitudinal  bundle,  155 
median  fissure  of  medulla,  39, 
318 
of  cord,  382 
nucleus  of  thalamus,  138 
orbital  gyrus,  73 
or  motor  root  of  spinal  nerves, 
418,419 


Anterior   perforated   substance,  37, 

79,  211 
pyramidal  tract,  102,  146,  242, 

319,  327,  407 
reticulo-spinal   fasciculus,    154, 

155.  233,  303,  309,  334,  407 
root-line  of  cord,  387 
spinal  artery,  376 
subarachnoid  space,  9,  373 
tecto-spinal  fasciculus,  155,  233, 

303,  331,  407 
tubercle  of  thalamus,  138 
Antero-lateral    fasciculus    proprius, 

405 

ganglionic  arteries,  20 
Antero-median   ganglionic    arteries, 

20 
Apertura  lateralis  ventriculi  quarti, 

9,  II,  323 
mediana  ventriculi  quarti,  9,  11, 

323 
Arachnoid  granulations,  6 

of  brain,  8 

and  cord  compared,  10 

of  spinal  cord,  373 

septum,  373 
Arbor  vitae  cerebelli,  286 
Archiplasm  sphere,  171 
Archipallium,  98 
Arcuate  nucleus  of  medulla,  338,  339 

of  thalamus,  222 
Arcus  occipito-parietalis,  63 
Area  parolfactoria,  93,  94,  95 

postrema,  360 
Arterial  circle  of  Willis,  14,  15 
Arteries  of  cerebellum,  26 

of  cerebrum,  15 

of  dura  mater,  6 

of  medulla,  23 

of  pia  mater,  13 


461 


462 


INDEX 


Arteries  of  pons,  25 
Association  centers  of  Flechsig,  186, 
193,  215,  216 
fibers  of  cerebellum,  290 
of  cerebrum,  253 
Atypical  cortex,  204 

neurones,  202 
Auditory  center,  68,  191 

paths,  445 
Aula  of  third  ventricle,  98,  127 
Axis    cylinder  processes,    167,    171, 

177 
Axones,  167,  171,  177 

of  cerebral  cortex,  204 


B 


Baillarger's  lines  or  zones,  198,  200, 

201,  204 
Base  of  brain,  35 

of  fore-brain,  71 
Basilar  plexus,  6 

vein,  22 
Basis  pedunculi,  37,  142,  143,  144 
Basket  cells,  279,  282 
Betz  cells,  202,  213,  214,  412 
Bipolar  neurones,  167,  175 
Biventral  lobules,  276 
Blood  supply  of  brain,  14 
of  cerebellum,  26 
of  cerebrum,  15 
of  medulla,  23 
of  pons,  25 
of  spinal  cord,  376 
Body  of  fornix,  108 
Borders  of  cerebral  hemisphere,  53 
Brachia  conjunctiva,  143,  160,  247, 
265,  287 
quadrigemina,  143,     164,     165, 
228 
Brachium  inferius,  164,  165,  228 
pontis,  38,  267,  288,  307 
superius,  164,  165,  228 
Brain    measurements    and  weights, 

47 
vesicles,  31 
Bundle  of  dorsal  horn  (Cajal),  397, 
406 


Cajal  neurones,  202 

Calamus  scriptorius,  360 

Calcar  avis,  91,  123 

Calcarine  fissure,  89 

Callosal  sulcus,  88 

Canalis  centralis  spinalis,  382 

Canals  of  Holmgren,  171 

Capsula  interna,  99,  124 

Capsular  radiation,  103 

Cauda  equina,  379 

Caudate  nucleus,  114,  116 

Cavernous  sinus,  6 

Cavum  septi  pellucidi,  no 

Cell  and  fiber  lamination  of  cerebral 

cortex,  195 
Centrifugal  arteries,  376 
Cellifugal  conduction,  173,  177 
Cellipetal  conduction,  174,  178 
Cells  of  anterior  columna,  389 

of  lateral  columna,  394 

of  posterior  columna,  396 
Center  of  abstract  concept,  60,  193 

of  concrete  concept,  194 

of  gray  crescent,  394 

of  intellectual  faculties,   260 

of  smell,  93,  94 

of  taste,  93,  98 
Central  gray  matter  of  cerebrum, 

235 

lobule,  272 

nucleus  of  thalamus,  223 

sulcus  of  Rolando,  56 

tegmental  tract,  305 
Centripetal  arteries,  376 
Centrum  semiovale,  188 
Cerebellar  notches,  35,  264 

reflexes,  454 

worm,  263 
Cerebello-fugal  fibers,  284 
Cerebello-petal  path,  290 
Cerebello-spinal  path,  333 
Cerebello-tegmental  fibers,  278,  284, 

286,  287,  290 
Cerebellum,  29,  30,  262 
Cerebral  aqueduct,  148 

circulation,  15 


INDEX 


463 


Cerebral  hemisphere,  263 

or  cranial  nerves,  361 

reflexes,  449 
Cerebro-pontal  paths,  430 
Cerebro-rubral  tract,  103 
Cerebro-spinal  fluid,  11,  iii 

or  pyramidal  paths,  427 

reflexes,  452 

tract,  102,  242 
Cerebrum,  29,  51 
Cervical  enlargement  of  cord,  380 
Chiasma  opticum,  37,  83 
Chorioid  epithelial  lamina,  126 
glands,  120 

plexus  of  fourth  ventricle,   11, 
323,  358 
of   lateral  ventricle,    11,  91, 

119,  126,  132 
of  third  ventricle,  11,  131,  132 

tela  of  fourth  ventricle,  11 
of  third  ventricle,  11,  12,  131, 
132 
Chorioidal  fissure,  80,  91,  119,  126 
Ciaglinski's  tract,  401 
Cilio-spinal  centers,  331 
Cingulate  sulcus,  87 
Cingulum  of  gyrus  fomicatus,  255 
Circular  sinus,  6 

sulcus  of  island,  70 
Circulation  of  rhombencephalon,  23 
Cisterna  ambiens  mesencephali,  91 
Claustrum,  115,  213 
Cochlear  path,  445 
Collateral  fissure,  81,  92 
Colliculi  of  corpora  quadrigemina, 

143,  164,  232,  234 
Colliculus  facialis,  294,  359 
Columna  anterior  of  cord,  389 

fomicis,  109,  136,  226 

lateralis,  394 

posterior,  395 
Columns,  see  Funiculi. 
Comma  tract  of  Schultze,  417 
Commissura  anterior  alba,  402 
cerebri,  132,  252 

grisea  spinalis,  387 

habenularum,  109,  132 

hippocampi,  108,  253,  257 


Commissura,     inferior     (Guddeni), 
232,  236 
posterior  cerebri,  130 
superior  (Meynerti),  232,  236 
Commissural  fibers  of  cerebrum,  251 
Commissuro-medullary     fasciculus, 

154 
Common  sensory  nuclei,  366 
Cone  of  growth,  181 
Confluens  sinum,  3 
Conus  medullaris,  382 
Convolutions,  see  Gyri. 
Cornu  anterius,  123 

-commissural  tract,  418 

inferius,  123 

posterius,  123 
Corona  radiata,  103 
Corpora  mammillaria,  37,  85,  236 

quadrigemina,  143 
Corpus  callosum,  104,  251 

dentatum,  284 

fomicis,  108 

geniculatum  laterale,  140 
mediale,  140 

medullare,  265,  286 

pineale,  131 

ponto-bulbare,  307,  337 

restiforme    or    corpora    resti- 
formia,  267,  289,  321,  336 

striatum,  98,  113,  217 

trapezoideum,  296 
Correlation  centers,  216 
Cortex  of  cerebellum,  278 

of  cerebrum,  186 

of  gyrus  cinguli,  212 

of  olfactory  bulb,  205 
tract,  211 
Cortical  fillet,  157,  228,  247,  249 

gray  matter  of  cerebrum,  1 86, 1 89 

system  of  arteries,  16 
Corticifugal  projection  fibers  of  cere- 
brum, 240 
Corticipetal  projection  fibers  of  cere- 
brum, 246 
Cortico-nuclear  fibers,  278 
Crossed  paralysis,  316 
Crus  fomicis,  108,  126 
Culmen  cerebelli,  272 


464 


INDEX 


Cuneo-lingual  gyrus,  9] 
Cuneus,  96 
Cuticle  plate,  31 
Cytoplasm,  169,  177 


Declive  monticuli,  272 
Decussatip  lemniscorum,  325 

pyramidum,  39,  325 
Decussation  of  brachia  conjunctiva, 

152 
Deep  intermediate  column,  394 
Defecation  reflexes,  448 
Degeneration  of  neurones  (Waller), 

180 
Deiter's  cells,  389 
Dendrites,  167,  174,  176 
Descending     postero-medial     tract, 

417 

posterolateral  tract,  418 
Diaphragma  sellae,  3 
Digitationes  hippocampi,  126 
Direct  cerebellar  tract,  289 

sensory  fasciculus  of  cerebellum, 
289 
Dorsal      longitudinal      bundle      of 
Schutz,  148,  237,  305 
spino- cerebellar  fasciculus,  289, 

336,  411 
tegmental  decussation,  152 
Dor  so- ventral  fibers  of  cord,  403 

of  medulla,  324,  326 
Dura  mater  of  brain,  i 
spinalis,  372 


Ectorhinal  sulcus,  81,  92 
Efferent  or  motor  paths,  427 
Embryologic  divisions  of  brain,  28 

method  of  locating  tracts,  404 
Eminentia  cinerea,  360 

collateralis,  92,  124 
Eminentiae  mediales,  323,  358 
Emissive  motor  area,  1 89 
End-arteries  of  Cohnheim,  18 
End-brain,  51,  52,  71 


Entry  zone  of  cord,  415 
Ependyma  cells,  167,  182 
Epicritic  extero-ceptors,  424,  425 
Epiphysis,  131 
Epipineal  recess,  131 
Equilibration  area,  192 
Equilibrium  reflexes,  453 
Experimental    method    of    locating 

tracts,  405 
External  arcuate  fibers  of  medulla, 
289,  319,  325,  326 

cerebellar  veins,  28 

veins  of  cerebrum,  22 
Evolution  of  brain,  260 

of  meninges,  i 


Facial  nerve,  42,  364 
Facies  cerebelli  inferior,  273 

superior,  269 
Falx  cerebelli,  2 

cerebri,  2 
Fascia  dentata,  82,  94,  95,  211 
Fasciculi,  bundles  or  tracts,  1 85 
Fasciculus  cerebro-spinalis,  146 
anterior,  327,  403,  407 
lateralis,  327,  328,  404,  412 
circum-olivaris,  307,  319,  337 
cuneatus,  417 
gracilis,  416 

longitudinalis  dorsalis,  (Schutzi) 
148,  151,  305 
inferior,  258 

medialis,  152,  301,  330,  406 
superior,  259 
mammillaris  princeps,   86,    109, 

249 
mammillo-tegmental,    86,    109, 

249 

mammillo-thalamic,     86,     109, 

249 

marginalis,  414 
obliquus  pontis,  293,  307,  338 
occipito-frontalis  inferior,  257 
proprius  anterior,  405 

lateral,  332,  405,  418 

posterior,  415,  418 


INDEX 


465 


Fasciculus  rubro-laquearis,  304 

spino-cerebellaris  dorsalis,  336 
ventralis,  333 

uncinatus,  258 

vestibulo-spinalis,  332,  408 
Fasciola  cinerea,  95 
Fastigial  commissure,  290 
Fastigio-bulbar  fasciculus,  286,  290 
Fastigium,  265,  358 
Feltwork  of  Kaes,  198,  202 
Fila  lateralia  pontis,  288,  296 
Fillet,  156 

decussation,  325 
Filum  terminale,  376,  379,  382 
Fimbria  hippocampi,  126 
Fimbrio-dentate  sulcus,  91 
First  type  neurone  (Deiter's),  171, 

178 
Fissura  (or  fissure),  53 

mediana  anterior,  382 
posterior,  382 

rhinalis,  92 
Fissure,  lateral  of  cerebrum,  55 

longitudinal  of  cerebrum,  54 

transverse  of  cerebellum,  35 
of  cerebrum,  33,  54 
Fissures  of  medial  surface  of  hemi- 
sphere, 35,  87 

of  medulla  oblongata,  317 

of  spinal  cord,  382 

of  tentorial  area,  80 
Flocculus,  275 

Floor  of  fourth  ventricle,  323,  358 
Foramen  interventriculare,  iii,  129 
Forceps  major,  106,  107,  123 

minor,  107 
Fore-brain,  29,  51,  52,  71 
Formatio  reticularis,  151,  298,  308 
Fornix,  108,  248,  256 

periphericus,  256 
Fossa  interpeduncularis,  142 

rhomboidea,  358 
Four  systems  of  common  afferent 

fibers,  424 
Fourth  ventricle,  318,  356 
Fovea  inferior,  323,  359 

superior,  295,  359 
Foveolae  granulares,  6 


Frontal  lobe  of  cerebrum,  36,  58,  72 

stalk  of  thalamus,  103,  228,  249 
Fronto-pontal  path,  430 
Fronto-pontal  tract,  103,   147,  241, 

430 
Function  of  cerebellum,  263,  282 
Functions  of  neurones,  179 
Funiculi  or  columns,  403 
Funiculus  anterior,  403 

cuneatus,  321,  335 

gracilis,  321,  335 

lateralis,  403,  404 

posterior,  403,  404 
Fusiform  bipolar  neurones,  1 75 

cells  of  cerebral  cortex,  202 

gyrus,  79,  81 


Ganglia  spinalia,  421 
Ganglion,  183,  362 

interpedunculare    or    n.    inter- 
peduncularis, 147 
terminale,  365 
Ganglionar  gray  matter  of  cerebel- 
lum, 284 
(nuclear)  gray  matter  of  cere- 
brum, 216 
Ganglionic  system  of  arteries,  18 
General  considerations  of  brain,  31 
Genetic  nuclei,   39,    184,   359,   362, 

370,  419 
Geniculate  bodies,  137,  140,  228 
Gennari's  line,  201 
Genu  of  corpus  callosum,  106 

of  internal  capsule,  100 
Germ  cells,  167 
Globus  pallidus,  114,  116 
Glomus  chorioideum,  119 
Glosso-palatine  nerve,  362 
Glosso-pharyngeal   nerve,    44,    326, 

364 

Golgi  cells,  389 

Gowers's  tract,  299 

Granule-cells  of  cerebellum,  280 

Gray  commissure  of  cord,  387,  400 
crescent  of  cord,  388 
matter  of  cerebellum,  275 


466 


INDEX 


Gray  matter  of  cerebrum,  i86 
of  medulla,  338 
of  pons,  305 
spinal  cord,  387 
Great  cerebral  vein  of  Galen,  21,  133 

middle  meningeal  artery,  7 
Grouping  of  neurones,  183 
Gustatory  center,  192 

nucleus  of  Nageotte,  338,  345 

paths,  446 

tract  or  radiation,  102,  161,  247, 
250,  302,  338 
Gyri  breves  insulae,  71 

of  frontal  lobe,  58 

of  island,  70 

of  medial  and  tentorial  surface, 
92 

of  occipital  lobe,  66 

of  parietal  lobe,  61 

of  temporal  lobe,  69 

of  tentorial  area,  79 

orbitales,  72 
Gyrus  cinguli,  93,  94 

circumambiens,  94 

diagonalis,  95 

fornicatus,  93,  94 

frontalis  superior,  96 

fusiformis,  97 

hippocampi,  93,  94 

intralimbicus,  82 

lingualis,  96 

longus  insulas,  71 

occipitalis  lateralis,  67,  69 
superior,  67 

orbitalis  lateralis,  73 
medialis,  73 

rectus,  73,  96 

semilunaris,  94 

subcallosus,  95,  106,  211 

subsplenialis,  95 

supracallosus,  95,  104 

transversus    insulae     of    Eber- 
staller,  71 


H 


Habenulo-peduncular  fasciculus,  249 
Hemiplegia  alterans,  216 


Hemispheria  cerebelli,  263 
Hiatus  capsulae,  99 
Hilus  nuclei  dentati,  285 

of  inferior  olivary  nucleus,  354 
Hind-brain,  262 
Hippocampal  gyrus,  79 

fissure,  80,  91 

formation,  126 

sulcus,  91 
Hippocampus,  91,  125 
Hippocampo-habenular     fasciculus, 

248,  256 
Hippocampo-mammillary      fascicu- 
lus, 248,  256 
Histogenesis  of  cerebellar  cortex  and 
nuclei,  282 

of  cerebral  cortex,  213 
Horizontal  sulcus  of  cerebellum,  268 
Horns  of  lateral  ventricle,  123 
H-shaped  column   of  gray  matter, 

388 
Hypoglossal  nerve,  47,  326,  365 

triangle,  360 
Hypophyseal  region,  36 
Hypophysis  cerebri,  37,  85 
Hypothalmo-striate  fasciculus,  219 
Hypothalamus,  83,  139,  235,  236 


I 


Incisura  cerebelli  anterior,  265 

posterior,  265 
Inferior  cerebellar  arteries  and  veins, 
26,  27,  28 
cerebral  veins,  22 
frontal  gyrus,  59 
horn  of  lateral  ventricle,  123 
lamina  of  internal  capsule,  100 
parietal  lobule,  64 
peduncle  of  cerebellum,  267 

of  thalamus,  100,  228 
petrosal  sinus,  6 
surface  of  cerebellum,  273 
temporal  gyrus,  70,  79 

sulcus,  81,  92 
view  of  brain,  35 
Inter-brain,  29,  51,  52,  71,  127 
Internalcapsule,  99,  124 


INDEX 


467 


Internal  cerebellar  veins,  28 
cerebral  veins,  20,  21,  133 
medullary  lamina  of  thalamus, 

220,  221 
vertebral  plexus  of  veins,  378 

Intermediate  nerve,  42,  363,  364 
olfactory  stria,  247 
spino-cerebellar  fasciculus,  300 
tract  or  path,  146,  219,  421,  430 

Intermedio-lateral  column  of  cells, 

394 
Intemuncial  fibers  of  corpus  stria- 
tum, 103 
Intero-ceptors,  424,  426 
Interparietal  sulcus,  62 
Interpeduncular  nucleus,  147 

space,  37 
Interpedunculo-tegmental  fasciculus, 

249 
Interventricular  foramen,  98,  129 
Intonation  center,  192 
Intumescentia  cervicalis,  380 

lumbalis,  382 
Island  (of  Reil),  70,  73 
Isthmus  of  gyrus  fornicatus,  93 

rhombencephali,    29,    30,    141, 
262 

K 

Key  and  Retzius's  apertures,  9 
L 

Lamina  affixa,  119 

chorioidea  epithelialis,  117,  126 

quadrigemina,  143,  164 

rostralis,  106 

terminalis,  37,  83,  135 
Large  pyramids  of  cerebral  cortex, 

200,  201 
Lateral  apertures  of  fourth  ventricle, 

9,11,323 
column   (or    funiculus)   of  me- 
dulla, 326,  327 

of  cord,  388,  394 
fasciculus  proprius,  320 
fillet,  157,  299 


Lateral  fissure  of  cerebrum  (Sylvian), 

55 
nucleus  of  thalamus,  223 
occipital  gyrus,  67 

sulcus,  66 
olfactory  stria,  247 
orbital  gyrus,  73 
pyramidal  tract,  102,  146,  242, 

319,  328,  412 
recess  of  fourth  ventricle,  322, 

358 
reticulo-spinal   fasciculus,    155, 

233,  303,  309,  334,  407 
tecto-spinal  fasciculus,  1 56,  233, 

303,  334,  409 

ventricles,  98,  no,  in 
Lemniscus,  156,  298,  299,  329 
Lentiform  nucleus,  114 
Ligamenta  denticulata,  373,  375 
Limbic  fissure,  92 

lobe,  82,  93,  94 
Limen  insulae,  70,  79 
Line  of  Baillarger,  198,  200,  201,  204, 
205,  214 

of  Gennari,  201,  205,  214 
Lingual  gyrus,  79,  81 
Lingula  cerebelli,  271 
Lipoid  granules,  171 
Lobe,  frontal,  58 

island  or  insula,  70 

limbic,  82,  93 

occipital,  65 

olfactory,  75 

parietal,  61 

temporal,  68 
Lobes  of  cerebellum,  271,  275 

of  cerebral  hemisphere,  58,  72, 
92,  98 
Lobulus  gracilis,  277 

paracentralis,  96 

quadrangularis,  272 
Lobus  centralis,  272 

culminis,  272 

declivis,  272 

folii  vermis,  273 

lingulae,  271 

noduli,  275 

pyramidis,  276 


468 


INDEX 


Lobus  pyriformis,  94 

tuberis,  276 

uvulae,  276 
Locus  caerulcus,  295,  359 
Long  association  fibers,  255 
Longitudinal  fibers  of  cord,  403 
of  medulla,  327 
of  pons,  297 

fissure  of  cerebrum,  33,  54 

striae,  95,  104 
Lumbar  enlargement  of  cord,  382 

puncture,  374 
Lushka's  apertures,  9 
Lymphatics  of  brain,  23 

of  cerebellum,  28 

of  cord,  378 
Lyre,  253 


M 


Magendie's  aperture,  9 
Mammillary  bodies,  37,  85,  236 
Marginal  fasciculus  of  Lissauer,  414 
Martinotti's  cells,  202 
Massa  intermedia,  137,  235,  237 
Masticator  nerve,  326 
Measurements  and  weights  of  brain, 

47,  48»  49,  50 
Medial  cerebral  veins,  22 

fillet,  157,247,298,325,329 
longitudinal  bundle,  152,  301, 

330,  406 
nucleus  of  thalamus,  222 
olfactory  stria,  248 
orbital  gyrus,  73 
ponto-spinal  tract  or  fasciculus, 

154 
Median  aperture  of  fourth  ventricle, 

9,11,323 

triangular   tract   of   Gambault 

and  Phillipe,  417 
ventricle  of  end-brain,  98 
Medium-sized  pyramids  of  cerebral 

cortex,  200 
Medulla  oblongata,  29,  30,  37,  262, 
316 
spinalis,  379 
Medullary  body  of  cerebellum,  365 


Medullary  laminae  of  cerebellum,  286 

stria  of  fourth  ventricle,  323 
of  thalamus,  109 

vela  of  cerebellum,  256,  266,  286 
Membranes  (meninges)  of  brain,  I 

of  spinal  cord,  372 
Mental  processes,  the  center  of,  51 
Mesencephalic  flexure,  32 

root  of  trigeminal  nerve,    162, 
302 
Mesencephalon,  29,  140,  141 
Metathalamus,  137,  140,  228 
Metencephalon,  29,  292 
Mid-brain,  29,  51,  140 
Middle  cerebral  artery,  17 

frontal  gyrus,  59 

peduncles   of   cerebellum,    267, 
288 

temporal  gyms,  69 
Mitochondria,  169 
Monkey's  brain,  45,  46 
Moss-like  appendages,  282 
Motor  center  or  area,  98,  189 

projection  fibers,  240 
Multipolar  neurones,  167,  169 
Muscle-sense,  436 
Myelin  sheath,  173,  178 


N 


Nageotte's  nucleus,  338,  345 
Naming  center,  192 
Neopallium,  98 
Nerves  of  arachnoid,  10 

of  dura  mater,  8 

of  pia  mater,  14 
Nervus  abducens,  42,  364 

accessorius,  44,  364 

acusticus,  42,  363 

facialis,  42,  364 

glossopharyngeus,  44,  364 

hypoglossus,  47,  365 

intermedius,  42,  363,  364 

oculomotorius,  41,  364 

olfactorii,  40,  363 

opticus,  41,  363 

terminalis,  365 

trigeminus,  41,  363,  364 


INDEX 


69 


Nervus  trochlearis,  41,  363 

vagus,  44,  364 
Neural  crests  or  ridges,  31 

groove,  31 

plate,  31 

tube,  32 
Neuraxone,  167,  171,  177 
Neuroblasts,  167 
Neurofibrillae,  169 
Neuroglia  cells,  167,  182 

of  cerebellum,  282 
Neurolemma,  173 
Neurone  doctrine,  178 

cycles,  184 
Neurones,  165,  166,  169,  170,  171, 

172 
Neuroplasm,  169 
Nigro-pontal  tract  or  fasciculus,  146, 

241 
Nissl  degeneration,  180 
Nodes  of  Ranvier,  174 
Nodule  of  cerebellum,  275 
Nuclear  or  ganglionar  gray  matter  of 
the  cerebellum,  284 
cerebrum,  216 
Nuclei  of  formatio  reticularis,  307, 

309 
of  thalamus,  220 
of  trigeminal  nerve,  309 
origines,  39,  184,  359.  362,  370, 

419 
terminales,  39,  yS,  84,  207,  311, 

345,  346,  348,  350,  365 
Nucleo-cerebellar     fasciculus,     161, 

288,  289 
Nucleus,  183 

ambiguus,  341 

amygdalae,  114,  117,  124,  209 

cardiacus,  342 

caudatus,  116 

centralis    superior,    medius   in- 
ferior, 309 

commissuralis,  338,  345 

dentatus,  284 

dorsalis  of  cord,  398 

emboliformis,  285 

fastigii,  285 

funiculi  cuneati,  351,  353 


Nucleus,  funiculi  gracilis,  351,  352 
globosus,  285 
habenulae,  138,  222 
hypothalamicus,  139,  147,  232 
interansalis,  100 
intercallatus,  341 
lateraHs  inferior,  324,  341 

medius,  309 

superior,  235 
lentiformis,  114 
of  abducent  nerve,  312 
of  ala  cinerea,  341,  342,  345 
of  anterior  tubercle,  221 
of  cochlear  nerve,  336,  350 
of  facial  nerve,  313 
of  hypoglossal  nerve,  341 
of   mesencephalic   root    of   tri- 
geminal nerve,  151,  239 
of  neurones,  168,  169,  177 
of  occulomotor  nerve,  150,  238 
of  pulvinar,  225 
of  trapezoid  body,  308 
of  trochlear  nerve,  150,  238 
of  vestibular  nerve,  315, 336,  348 
olivarus  inferior,  354 
originis,  39,  184,  359,  362,  370, 

419 
pontis,  296,  297,  305,  306 
ponto-bulbaris,  307,  337 
praeolivaris,  308 
ruber,  139 
salivarius,  314,  344 
tegmenti  dorsalis,  152 
tegmenti  profundus,  151,  235 
terminalis,  39,  76,  84,  207,  311, 

345,  346,  348,  350,  365 
tractus  solitarii,  338,  345 

spinalis  nervi  trigemini,  346 


Obex,  322 
Occipital  lobe,  65 

sinus,  4 
Occipito-parietal  sulcus,  57,  89 
Occipito-thalamic  fibers,  229 
Ocular  reflexes,  156 
Oculomotor  nerve,  41,  364 

nucleus,  238 


470 


INDEX 


Olfacto-amygdalate  fasciculus,  247 
Olf acto-habenular  fasciculus,  248 
Olfacto-hippocampal  fasciculus,  247, 

256 
Olfacto-mesencephalic       fasciculus, 

236,  248 
Olfactory  bulb,  36,  75 

center  or  area,  192 

cortex,  205 

ganglion,  40 

islets,  209 

lobe,  75 

nerves,  40,  207,  363 

path,  441 

projection  fibers,  247 

sulcus,  72 

striae,  76,  247 

tract,  76,  207 

triangle,  78 
Olivary  group  of  nuclei,  307 

nuclei,  inferior,  329,  354 

pedicle,  307 
Olive  (oliva),  39,  320 
Olivo-arcuate  migration,  339,  355 
Olivo-cerebellar  fasciculus,  289,  325, 

354 
Optic  center  or  area,  192,  204 

chiasma,  37,  83 

nerves,  37,  84,  363,  443 

path,  443 

radiation,  102,  228,  247,  250 

recess,  135 

reflex  center,  164 
tract,  233 

tracts,  37,  84,  363,  443 
Orbital  sulci,  72 
Orders  of  neurones,  179 
Organ  of  cell  division,  171 
Orientation  center  or  area,  192 
Origin  of  cerebral  or  cranial  nerves, 
361 

of  medulla,  317 
Oval  tract  of  Flechsig,  417 


Pineal  body,  131 
recess,  131 


Plaques  or  placodes,  175 

Plexifol-m  layer  of  cortex,  198 

Plexus  chorioideus  of  lateral  ven- 
tricle, 119 
ventriculi  quarti,  11,  323 
tertii,  131 

Pole  of  island,  70 

Poles  of  hemisphere,  52 

Pons,  29,  30,  37,  262,  292 

Pontine  flexure,  32 

Post-central    sulcus    of   cerebellum, 
269 

Post-declivil  sulcus,  271 

Posterior  central  gyrus,  62 

cerebellar  commissure,  290 
cerebral  artery,  17 
chorioidal  arteries,  18 
column  of  medulla,  327 
columna  of  cord,  388,  395 

of  gray  matter,  344 
commissure,  130 
fasciculus  proprius,  418 
horn  of  lateral  ventricle,  123 
inferior  cerebellar  artery,  27 
intermediate  sulcus,  387 
lateral  sulcus,  39,  318,  385 
median  fissure  of  cord,  382 
orbital  gyrus,  73 
or  sensory  root  of  spinal  nerve, 

420 
perforated  substance,   37,    142, 

147 

spinal  artery,  376 

subarachnoid  space,  9,  373 

view  of  cerebrum,  33 
Postero-lateral    ganglionic    arteries, 

20 
Postero-median  ganglionic  arteries, 

20 
Post-nodular  sulcus,  273 
Post-parietal  gyrus,  65 
Post-pyramidal  sulcus,  274 
Posture  reflexes,  457 
Praecuneus,  96 

Precentral  sulcus  of  cerebellum,  269 
Precommissural  body,  253 
Predeclivil  sulcus,  269 
Prepyramidal  sulcus,  274 


INDEX 


471 


Projection  fibers  of  cerebellum,  287 

of  cerebum,  240 
Proprio-ceptors,  424 
Proscencephalon,  29,  52 
Protopathic  extero-ceptors,  424,  425 
Protoplasmic  loops  and  plexuses  of 

neurones,  422 
Psychic  acustic  area  or  center,  69, 
192 

auditory  center,  69,  192 

motor  region,  98,  190 

optic  area  or  center,  192 

region,  98 

sensory  area  or  center,  190 
Pulvinar  of  thalamus,  137 
Pupillary  contraction,  451,  454 

dilitation,  454 

reflexes,  454 
Pupillo-dilator  tract,  233,  331 
Purkinje's  cells,  278 
Putamen,  115 
Pyramid,  39,  276,  319,  327 
Pyramidal  decussation,  325 

Q 

Quadrigeminal  lamina  (tectum)  143, 

164 
Quadrangular  lobule,  272 


Radiatio  corporis  callosi,  251 
Radiation  of  cerebral  cortex,  204 
Recessus  triangularis,  127,  133 
Red  nucleus,  139,  229 
Reflex  area,  185,  448 

mechanism  of  spinal  cord,  393 

paths,  447 
Regeneration  of  neurones,  180 
Respiratory  reflexes,  452 
Restiform  body,  39,  267,  289,  321, 

336 
Reticulo-cerebellar  fasciculus,  289 
Reticulo-spinal  fasciculi,    154,    155, 

233,  303,  309,  334,  407 
path,  433 
Retro-lentif  orm  part  of  internal  cap- 
sule, lOI 


Rhinencephalon,  73,  94,  96,  98 
Rhombencephalon,  29,  37,  262 
Ribot's  law  of  regression,  51 
Roof  epithelium  of  fourth  ventricle, 
322 
of  third  ventricle,  131 
Root  of  hypoglossal  nerve,  326 
Roots  of  cerebral  (cranial)  nerves,  39 

of  spinal  nerves,  418 
Rostrum  of  corpus  callosum,  100 
Rubro-reticular  fasciculus,  304 
Rubro-spinal   fasciculus,    161,    229, 

304,  333,  409,  413 
path,  432 
Rubro- thalamic  fasciculus,  l6l,  229 


Salivary  nucleus,  314,  344 

Sagittal  sinuses,  3 

Second  type  neurone   (Golgi)    171, 

178 
Semilunar  lobules,  273,  276 
Sense  of  touch,  436 
Sensory  area,  190 

projection  fibers  of  cerebrum, 
246 

root  of  trigeminal  nerve,  347 
Septo-marginal  tract  of  Bruce  and 

Muir,  417 
Septum  pellucidum,  95,  109,  211 
Short  association  fibers,  253 
Sinuses  of  dura  mater,  3 
Slender  lobules,  276 
Small  pyramids  of  cortex,  198 
Smelling  brain,  73 
Solitary  cells  of  Meynert,  205 

tract,  338 
Somaesthetic  area,  62,  98,  191 
Somatic  area  of  cortex,  215,  216 

nuclei,  150,  183,  184,  310,  342, 
345,  346,  348,  353,  365,  370, 
388,389,  397,  419,  421  . 
Special  sense  fasciculi,  250 
nuclei,  367 

sensations,  441 
Speech  center,  60 
Spheno-parietal  sinus,  6 


472 


INDEX 


Spinal  bulb,  316 

cord,  379 

ganglion,  420,  421 

reflexes,  448 

tract  of  trigeminal  nerve,  302, 
321,  335 
Spino-cerebral  reflexes,  452 
Spino- olivary    tract    or    fasciculus, 

332,411 
Spino-reticular  fasciculus,  409 
Spino-tectal  fasciculus,  300,  410 
Spino-thalamic  fasciculus  or  tract, 
159,  247,  299,  320,  333,  410 
Spino-vestibular  tract  or  fasciculus, 

412 
Splenium  of  corpus  callosum,  106 
Spongioblasts,  167 
Stepping  reflexes,  458 
Stellate  cells  of  cerebellum,  279 

or  polymorphous  cells  of  cere- 
brum, 201 
Stereognosis,  436 
Stereognostic  center,  64,  98,  190 
Straight  sinus,  4 
Stratum  cinereum,  278 

gangliosum,  280 

griseum  centrale,  148,  235,  237 

interolivare  lemnisci,  325 
Stria  medularis  thalami,  132,  226 

terminalis,  117,  124 
Strio-fugal  tracts,  100,  218,  241 
Strio-hypothalamic  tract,  100,  218, 

241 
Strio-nigral  tract,  100,  146,  219,  241 
Strio-petal  tracts,  218 
Strio-rubro  tract,  100,  218,  241 
Strio- thalamic  tract,  100,  218,  241 
Structure  and  relation  of  pia  mater, 

ID 

of  cerebrum,  165 

of  pons,  295 
Subarachnoid  fluid,  9 

rivulets,  9 

spaces,  9,  373 
Subiculum  hippocampi,  209 
Subparietal  point,  56 
Substantia  alba  cerebri,  239 
spinalis,  387 


Substantia,  gelatinosa  spinalis,  388, 
396 

grisea  cerebri,  186 
spinalis,  387 

nigra,  143,  147,  235 

perforata  anterior,  211 
posterior,  147 

reticularis,  324,  329 

spongiosa,  388 
Sulci,  53,  54 

of  frontal  lobe,  58 

of  inferior  surface  of  cerebellum, 
.      273 

of   medial   surface   of   cerebral 
hemisphere,  87 

of  medtilla,  318 

of  occipital  lobe,  66 

of  orbital  surface,  72 

of  parietal  lobe,  61 

of  tentorial  area,  80 

of  temporal  lobe,  69 

of  upper  surface  of  cerebellum, 
269 

parolfactory,  78 
Sulcus  central  of  island,  70 

centralis  Rolandi,  56 

cinguli,  87 

circularis  insulae,  70 

hypothalamicus,  135 

intermedius  anterior,  387 
posterior,  387 
prosencephali,  117 

lateralis  mesencephali,  142 

limitans,  294,  323,  359 

lingualis,  97 

nervi  oculomotorii,  143 

occipito-parietalis,  57 

olfactory,  72 

paracingularis,  96 

post-centralis  cerebelli,  269 

post-declivis,  271 

post-nodularis,  273 

post-pyramidalis,  274 

pracentralis  cerebelli,  269 

praedeclivis,  269 

praepyramidalis,  274 

rostralis,  96 

subparietalis,  87 


INDEX 


473 


Sulcus  subrostralis,  96 

vallectUae,  273 
Superficial  middle  cerebral  vein,  23 
Superior  cerebellar  artery,  27 

cerebral  veins,  22 

fillet,  157,  298 

frontal  gyrus,  59 

medullary  velum,  143,  287,  288 

occipital  gyrus,  67 

olivary  nucleus,  307 

parietal  lobule,  62 

peduncles   of   cerebellum,    160, 
265,  287 

petrosal  sinus,  6 

temporal  gyrus,  69 

view  of  brain,  33 
Supramarginal  gyrus,  65 
Surface  of  cerebellum,  inferior,  273 

superior,  269 
Surfaces  of  cerebral  hemisphere,  53 

of  medulla,  318,  319,  320,  321, 
322,  323 

of  mid-brain,  141 

of  pons,  293 

of  spinal  cord,  382 
Sustentacular  tissue,  182 
Swimming  reflexes,  456 
Sylvian  point,  56 
Synapses,  186 


Taenia  of  fourth  ventricle,  322,  323 

pontis,  288 
Tactile  sensations,  436 
Tapetum,  124,  259 
Tassel  cells,  209 

Tecto-cerebellar  fasciculi,  233,  288 
Tecto-pontal  fasciculi,  234 
Tecto-reticular  fasciculi,  234 
Tecto-spinal  fasciculi,  155,  156,  232, 

303 
Tectum,  143 
Tegmental  decussations,  152 

part  of  hypothalamus,  139 
Tegmentum,  143,  147 
Tela  chorioidea  ventriculi  quarti,  1 1 

tertii,  11 


Telodendrion  or  end-brush,  172 
Temperature  impulses,  436 
Temporal  lobes  of  cerebrum,  36,  68 
Temporo-pontal  path,  430 

tract,  100,  146,  241 
Temporo-thalamic  fibers,  102,  229 
Tentorium  cerebelli,  2 
Terminal  nuclei,  39,  184,  359,  362, 

365,  420 
nerve,  365 
Thalamo-cortical  paths  for  common 

sensory  impulses,  225 
Thalamo- occipital  fibers,  228 
Thalamo- olivary  fasciculus,  161, 304, 

332,  334 
Thalamo-spinal  fasciculus,  161,  305, 

334,  409,  413 
Thalamo-striate  fasciculus,  219 
Thalamo- tem-poral  fibers,  loi,  229 
Thalamus,  119,  136,  220,  433 

as  a  center  of  consciousness,  433 
Third  ventricle,  98,  127 
Tigroid  or  Nissl  substance,  171 
Tonsils,  276 

Tracing  of  impulses,  427 
Tracts,  bundles  or  fasciculi,  185 

of  posterior  columns  of  cord,  415 

of  spinal  cord,  405 

of  the  tegmentum,  152 
Tractus  cerebrorubricus,  103 

fronto-pontalis,  147 

intermedius,  146 

temporo-pontalis,  146 

solitarius,  338 

spinalis  n.  trigemini,  302,  321, 

335 
Transverse  fibers  of  cord,  402 
of  medulla,  324 
of  pons,  295 
fissure  of  cerebellum,  35 

of  cerebrum,  33,  354 
occipital  sulcus,  67 
sinuses,  5 

temporal  gyri  of  Heschl,  68 
Trapezoid  body,  296 
Triangle     of    habenula     (trigonum 
habenulae),  137 
of  lateral  fillet,  148,  165 


474 


INDEX 


Triangiilar  tract  of  Helwig,  332 
Trigeminal  nerve  roots,  38,  41,  302, 

363,  364 

nuclei,  151,  239,  309,  310,  311 

nucleus  of  mid-brain,  151,  239 
Trigonum  collaterale,  123 

hypoglossi,  360 

lemnisci,  148,  165 

olfactorium,  211 

vagi,  323,  360 
Trochlear  nerve,  41,  143,  364 

nucleus,  150,  238 
Truncus  of  corpus  callosum,  106 
Tuber  cinereum,  37,  84 

vermis,  276 
Tuberculum  acusticum,  351 

anterius  thalami,  138 
Types  of  neurones,  178 


U 


Uncinate  fasciculus,  257,  258 
Uncus,  94,  207 
Uvula,  276 


Vallectda  cerebelli,  35,  264,  273 
Valve  of  Vieussens,  266 
Vagus  nerve,  44,  326,  364 
Veins  of  cerebellum,  28 
of  cerebrum,  20 
of  medulla,  25 
of  pia  mater,  14 
of  pons,  26 
of  spinal  cord,  378 
Velum  interpositum,  132 
meduUare  inferius,  265 
superius,  266 
Vena  terminalis,  117 
Venae  cerebri  internae,  117 
spinales  externas,  378 
internae,  378 
Ventral   spino-cerebellar  fasciculus, 
or  tract,  295,  300,  320,  333, 
410 


Ventral  stalk  of  thalamus,  100,  226, 
249 

tegmental  decussation,  152 
Ventricle  of  spinal  cord,  382 
Ventricles,  33 

of  fore-brain,  98 
Ventricular  gray  matter  of  cerebrum, 

235 

Ventriculus  lateralis,  1 1 1 
quartus,  356 
terminalis,  382 
tertius,  127 
Vermis  cerebelli,  263 
Vestibular  arc  of  equilibrium,  290, 
332 
nerve,  326,  362 
path,  445 
Vestibulo-spinal  fasciculus  or  tract, 

320,  332,  408 
Vincula  cerebelli,  271 
Visceral  afferent  tract,  336 
area  of  cortex,  215 
nuclei,  150,  183,  184,  315,  342, 
345,  365,  370,  388,  395.  397, 
398,  419,  421 
paths  to  cerebellum,  459,  460 
Visual  center,  81,  97,  98,  204 


W 


Wallenberg's  bundle,  236 
Wallerian  degeneration,  180 
Weight  of  brain,  52 
White  anterior  commissure  of  cord, 
402 
matter  of  cerebellum,  286 

of  cerebrum,  239  ^ 

of  pons,  295 

of  medulla,  323 

of  spinal  cord,  387,  402 

of  thalamus,  225 


Zona  incerta,  139 

Zonal  layer  of  cortex,  196,  197,  198, 
200 


6353364 


3  1378  00635  3364 


RETURN  TO  the  circulation  desk  of  any 
University  of  California  Library 
or  to  the 
NORTHERN  REGIONAL  LIBRARY  FACILITY 
Bldg.  400,  Richmond  Field  Station 
University  of  California 
Richmond,  CA  94804-4698 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 

•  2-month  loans  may  be  renewed  by  calling 
(510)642-6753 

•  1  -year  loans  may  be  recharged  by  bringing 
books  to  NRLF 

•  Renewals  and  recharges  may  be  made  4 
days  prior  to  due  date. 


DUE  AS  STAMPED  BELOW 

jJUMJ  01998 

JUT.  (r9  mnm 

RETURNED 

JUL  1 4  1997 

^^«*.-.   -^ 

12,000(11/95) 

ls4)4128 


